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finish zfs incident

2026-01-04 01:14:00 +01:00

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First ZFS Degradation

Problem

On 2025-12-30 I was snooping around the Proxmox UI where I accidentally bumped into a storage view that showed that my ZFS pool (which I use for the disks of all my VMs) was in degraded state. Opening up the detail, it appeared one of the disks was in FAULTED state.

I attempted rebooting the host, which triggered an attempt at resilvering. But the disk remained in the same state.

First diagnostic

After researching a bit, I ran the following diagnostic steps:

I scanned the kernel logs with dmesg -T | egrep -i 'ata[0-9]|sata|reset|link|i/o error|blk_update_request|scsi|sense' | tail -200.
- The logs revealed that the disk connection seemed flaky, with the device reconnecting and going from bein sdb to sdc. Also, speed was being downgraded sequentially.
I ran the smartctl health assessment and the smartctl short test.
- This revealed that the disk looked healthy, and that it was having repeated "Hardware resets". Apparently, this is consistent with the idea that the HDD is repeteadly connecing/disconnecting, as the kernel logs point to.

So, after these, the initial hypothesis is that the drive itself is in good shape, but there is a connection issue. The first candidates are that either the SATA data cable is not working properly, or the power supply to the disk is flickering. If that's not the case, the issue could lie in the SATA port in the motherbase, or some other motherbase issue upstream of the sata port. Finally, it could also be an issue in the PSU.

First solution attempt

Plan

With this info, I decide to try to reseat the HDD as a first solution.

Rough plan:

Pre-action
- Take some vars in:
```
DISKID="$(ls -1 /dev/disk/by-id/ | grep -m1 WX11TN0Z)"
echo "$DISKID"
DISKPATH="/dev/disk/by-id/$DISKID"
echo "$DISKPATH"
```
- Log:
  - Serial of the bad drive
  - ZFS status: zpool status -v proxmox-tank-1
  - Kernel log after boot and some minutes of normal operation: dmesg -T | egrep -i 'ata4|sata|reset|link|exception|interface fatal|failed to IDENTIFY|qc timeout|I/O error|blk_update_request|Not Ready' | tail -200
  - Smartctl output:
```
readlink -f "$DISKPATH"
smartctl -x "$(readlink -f "$DISKPATH")" | egrep -i 'overall|Reallocated|Pending|Offline_Uncorrect|CRC|Error Log|Hardware Resets|COMRESET|SATA Phy'
```
- Reseat
  - Remove the disk from the ZFS pool
    - Turn it off with zpool offline proxmox-tank-1 "$DISKID"
    - Check with zpool status -v proxmox-tank-1
  - Power down the server
  - Open up, check the disks. Map out the relation between the name tags and the serial numbers.
  - Reseat both the power cable and the data cable of the faulty disk.
  - Since we opened up, also check the cables of the other unit.
  - Close again, reboot.
- Taking back online and evaluating
  - First, check that the OS sees the disk properly:
```
ls -l /dev/disk/by-id/ | grep WX11TN0Z
readlink -f "$DISKPATH"
```
  - Start a terminal dedicated to monitoring kernel logs with dmesg -Tw. Leave it running while we go for next steps.
  - If the disk appears properly and there are no weird signals in kernel logs, add it back into the ZFS pool. Monitor the resilvering process regularly with zpool status, and wait for resilvering to finish:
```
zpool online proxmox-tank-1 "$DISKID"
zpool status -v proxmox-tank-1
```
  - Run a scrub and monitor the disk state while it happens. Also, pay special attention to the kernel log output, we shouldn't see any SATA resets. The scrub can take an hour or two.
```
zpool scrub proxmox-tank-1
watch -n 5 "zpool status -v proxmox-tank-1"
```
  - If ZFS shows no problems, after ~30min of activity, check again with smartctl to evaluate disk health and confirm it's all good:
```
smartctl -x "$(readlink -f "$DISKPATH")" | egrep -i 'Reallocated|Pending|Offline_Uncorrect|CRC|Hardware Resets|COMRESET|SATA Phy'
```
- Decision:
  - If outcome was like this:
    - No weird kernel log messages.
    - ZFS indicates healthy status after resilvering, holds it consistently.
    - smartctl reads that disk is healthy.
  - Then disk is healthy, cable connection was solved and we're all good.
  - If any of the previous was not successful, we're still in trouble. Given outputs, evaluate if we should judge cables, disk or motherboard next.

Execution notes

Pre shutdown logs

Disk ID:

DISKID="ata-ST4000NT001-3M2101_WX11TN0Z"
DISKPATH="/dev/disk/by-id/ata-ST4000NT001-3M2101_WX11TN0Z"

ZFS Pool status with zpool status -v proxmox-tank-1:

  pool: proxmox-tank-1
state: DEGRADED
status: One or more devices is currently being resilvered.  The pool will
  continue to function, possibly in a degraded state.
action: Wait for the resilver to complete.
  scan: resilver in progress since Fri Jan  2 22:25:31 2026
  978G / 1.26T scanned at 1.92G/s, 26.0G / 524G issued at 52.3M/s
  0B resilvered, 4.96% done, no estimated completion time
config:

  NAME                                 STATE     READ WRITE CKSUM
  proxmox-tank-1                       DEGRADED     0     0     0
    mirror-0                           DEGRADED     0     0     0
      ata-ST4000NT001-3M2101_WX11TN0Z  FAULTED    108   639   129  too many errors
      ata-ST4000NT001-3M2101_WX11TN2P  ONLINE       0     0     0

errors: No known data errors

Kernel logs coming from a clean boot after around 10 min of operation:

sudo dmesg -T | egrep -i 'ata4|sata|reset|link|exception|interface fatal|failed to IDENTIFY|qc timeout|I/O error|blk_update_request|Not Ready' | tail -200
[Fri Jan  2 22:25:08 2026] ata4.00: ATA-11: ST4000NT001-3M2101, EN01, max UDMA/133
[Fri Jan  2 22:25:08 2026] ata4.00: 7814037168 sectors, multi 16: LBA48 NCQ (depth 32), AA
[Fri Jan  2 22:25:08 2026] ata4.00: Features: NCQ-sndrcv
[Fri Jan  2 22:25:08 2026] ata4.00: configured for UDMA/133
[Fri Jan  2 22:25:13 2026] ata4.00: exception Emask 0x50 SAct 0x70220001 SErr 0xe0802 action 0x6 frozen
[Fri Jan  2 22:25:13 2026] ata4.00: irq_stat 0x08000000, interface fatal error
[Fri Jan  2 22:25:13 2026] ata4: SError: { RecovComm HostInt PHYInt CommWake 10B8B }
[Fri Jan  2 22:25:13 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:13 2026] ata4.00: cmd 60/20:00:98:4e:04/00:00:38:00:00/40 tag 0 ncq dma 16384 in
[Fri Jan  2 22:25:13 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:13 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:13 2026] ata4.00: cmd 60/00:88:d8:39:00/01:00:38:00:00/40 tag 17 ncq dma 131072 in
[Fri Jan  2 22:25:13 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:13 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:13 2026] ata4.00: cmd 60/20:a8:98:49:04/00:00:38:00:00/40 tag 21 ncq dma 16384 in
[Fri Jan  2 22:25:13 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:13 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:13 2026] ata4.00: cmd 60/18:e0:a8:26:d4/00:00:38:00:00/40 tag 28 ncq dma 12288 in
[Fri Jan  2 22:25:13 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:13 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:13 2026] ata4.00: cmd 60/30:e8:e8:ad:d5/00:00:38:00:00/40 tag 29 ncq dma 24576 in
[Fri Jan  2 22:25:13 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:13 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:13 2026] ata4.00: cmd 60/00:f0:00:2a:00/01:00:38:00:00/40 tag 30 ncq dma 131072 in
[Fri Jan  2 22:25:13 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:13 2026] ata4: hard resetting link
[Fri Jan  2 22:25:14 2026] ata4: SATA link down (SStatus 0 SControl 300)
[Fri Jan  2 22:25:14 2026] ata4: hard resetting link
[Fri Jan  2 22:25:19 2026] ata4: link is slow to respond, please be patient (ready=0)
[Fri Jan  2 22:25:24 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:25:24 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:25:24 2026] ata4: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[Fri Jan  2 22:25:29 2026] ata4.00: qc timeout after 5000 msecs (cmd 0xec)
[Fri Jan  2 22:25:29 2026] ata4.00: failed to IDENTIFY (I/O error, err_mask=0x4)
[Fri Jan  2 22:25:29 2026] ata4.00: revalidation failed (errno=-5)
[Fri Jan  2 22:25:29 2026] ata4: limiting SATA link speed to 3.0 Gbps
[Fri Jan  2 22:25:29 2026] ata4: hard resetting link
[Fri Jan  2 22:25:30 2026] ata4: SATA link up 3.0 Gbps (SStatus 123 SControl 320)
[Fri Jan  2 22:25:30 2026] ata4.00: configured for UDMA/133
[Fri Jan  2 22:25:30 2026] ata4: EH complete
[Fri Jan  2 22:25:33 2026] ata4.00: exception Emask 0x50 SAct 0x30008000 SErr 0xe0802 action 0x6 frozen
[Fri Jan  2 22:25:33 2026] ata4.00: irq_stat 0x08000000, interface fatal error
[Fri Jan  2 22:25:33 2026] ata4: SError: { RecovComm HostInt PHYInt CommWake 10B8B }
[Fri Jan  2 22:25:33 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:33 2026] ata4.00: cmd 60/a0:78:30:92:54/00:00:a2:00:00/40 tag 15 ncq dma 81920 in
[Fri Jan  2 22:25:33 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:33 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:33 2026] ata4.00: cmd 60/40:e0:50:ae:11/00:00:a0:00:00/40 tag 28 ncq dma 32768 in
[Fri Jan  2 22:25:33 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:33 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:33 2026] ata4.00: cmd 60/68:e8:30:0f:59/02:00:a2:00:00/40 tag 29 ncq dma 315392 in
[Fri Jan  2 22:25:33 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:33 2026] ata4: hard resetting link
[Fri Jan  2 22:25:34 2026] ata4: SATA link down (SStatus 0 SControl 320)
[Fri Jan  2 22:25:34 2026] ata4: hard resetting link
[Fri Jan  2 22:25:39 2026] ata4: link is slow to respond, please be patient (ready=0)
[Fri Jan  2 22:25:44 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:25:44 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:25:44 2026] ata4: SATA link up 3.0 Gbps (SStatus 123 SControl 320)
[Fri Jan  2 22:25:49 2026] ata4.00: qc timeout after 5000 msecs (cmd 0xec)
[Fri Jan  2 22:25:49 2026] ata4.00: failed to IDENTIFY (I/O error, err_mask=0x4)
[Fri Jan  2 22:25:49 2026] ata4.00: revalidation failed (errno=-5)
[Fri Jan  2 22:25:49 2026] ata4: limiting SATA link speed to 1.5 Gbps
[Fri Jan  2 22:25:49 2026] ata4: hard resetting link
[Fri Jan  2 22:25:50 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:25:50 2026] ata4.00: configured for UDMA/133
[Fri Jan  2 22:25:50 2026] ata4.00: limiting speed to UDMA/100:PIO4
[Fri Jan  2 22:25:51 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:25:51 2026] ata4.00: configured for UDMA/100
[Fri Jan  2 22:25:51 2026] ata4: EH complete
[Fri Jan  2 22:25:52 2026] ata4.00: exception Emask 0x50 SAct 0x80001001 SErr 0x20802 action 0x6 frozen
[Fri Jan  2 22:25:52 2026] ata4.00: irq_stat 0x08000000, interface fatal error
[Fri Jan  2 22:25:52 2026] ata4: SError: { RecovComm HostInt PHYInt }
[Fri Jan  2 22:25:52 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:52 2026] ata4.00: cmd 60/b8:00:c0:31:57/00:00:94:00:00/40 tag 0 ncq dma 94208 in
[Fri Jan  2 22:25:52 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:52 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:52 2026] ata4.00: cmd 60/58:60:c0:73:45/00:00:94:00:00/40 tag 12 ncq dma 45056 in
[Fri Jan  2 22:25:52 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:52 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:25:52 2026] ata4.00: cmd 60/58:f8:08:72:45/00:00:94:00:00/40 tag 31 ncq dma 45056 in
[Fri Jan  2 22:25:52 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:25:52 2026] ata4: hard resetting link
[Fri Jan  2 22:25:52 2026] ata4: SATA link down (SStatus 0 SControl 310)
[Fri Jan  2 22:25:52 2026] ata4: hard resetting link
[Fri Jan  2 22:25:57 2026] ata4: link is slow to respond, please be patient (ready=0)
[Fri Jan  2 22:26:02 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:26:02 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:26:02 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:26:08 2026] ata4.00: qc timeout after 5000 msecs (cmd 0xec)
[Fri Jan  2 22:26:08 2026] ata4.00: failed to IDENTIFY (I/O error, err_mask=0x4)
[Fri Jan  2 22:26:08 2026] ata4.00: revalidation failed (errno=-5)
[Fri Jan  2 22:26:08 2026] ata4: hard resetting link
[Fri Jan  2 22:26:08 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:26:08 2026] ata4.00: configured for UDMA/100
[Fri Jan  2 22:26:08 2026] ata4: EH complete
[Fri Jan  2 22:26:10 2026] ata4.00: exception Emask 0x50 SAct 0x1800200 SErr 0x60802 action 0x6 frozen
[Fri Jan  2 22:26:10 2026] ata4.00: irq_stat 0x08000000, interface fatal error
[Fri Jan  2 22:26:10 2026] ata4: SError: { RecovComm HostInt PHYInt CommWake }
[Fri Jan  2 22:26:10 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:26:10 2026] ata4.00: cmd 60/58:48:40:00:09/00:00:7b:00:00/40 tag 9 ncq dma 45056 in
[Fri Jan  2 22:26:10 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:26:10 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:26:10 2026] ata4.00: cmd 60/40:b8:38:53:18/00:00:86:00:00/40 tag 23 ncq dma 32768 in
[Fri Jan  2 22:26:10 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:26:10 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:26:10 2026] ata4.00: cmd 60/58:c0:90:0f:0e/00:00:7f:00:00/40 tag 24 ncq dma 45056 in
[Fri Jan  2 22:26:10 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:26:10 2026] ata4: hard resetting link
[Fri Jan  2 22:26:10 2026] ata4: SATA link down (SStatus 0 SControl 310)
[Fri Jan  2 22:26:10 2026] ata4: hard resetting link
[Fri Jan  2 22:26:15 2026] ata4: link is slow to respond, please be patient (ready=0)
[Fri Jan  2 22:26:20 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:26:20 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:26:20 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:26:26 2026] ata4.00: qc timeout after 5000 msecs (cmd 0xec)
[Fri Jan  2 22:26:26 2026] ata4.00: failed to IDENTIFY (I/O error, err_mask=0x4)
[Fri Jan  2 22:26:26 2026] ata4.00: revalidation failed (errno=-5)
[Fri Jan  2 22:26:26 2026] ata4: hard resetting link
[Fri Jan  2 22:26:26 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:26:26 2026] ata4.00: configured for UDMA/100
[Fri Jan  2 22:26:26 2026] ata4.00: limiting speed to UDMA/33:PIO4
[Fri Jan  2 22:26:27 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:26:27 2026] ata4.00: configured for UDMA/33
[Fri Jan  2 22:26:27 2026] ata4: EH complete
[Fri Jan  2 22:26:28 2026] ata4.00: exception Emask 0x50 SAct 0x800003 SErr 0x20802 action 0x6 frozen
[Fri Jan  2 22:26:28 2026] ata4.00: irq_stat 0x08000000, interface fatal error
[Fri Jan  2 22:26:28 2026] ata4: SError: { RecovComm HostInt PHYInt }
[Fri Jan  2 22:26:28 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:26:28 2026] ata4.00: cmd 60/58:00:f0:f8:23/00:00:ab:00:00/40 tag 0 ncq dma 45056 in
[Fri Jan  2 22:26:28 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:26:28 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:26:28 2026] ata4.00: cmd 60/58:08:80:fa:23/00:00:ab:00:00/40 tag 1 ncq dma 45056 in
[Fri Jan  2 22:26:28 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:26:28 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:26:28 2026] ata4.00: cmd 60/50:b8:48:f8:23/00:00:ab:00:00/40 tag 23 ncq dma 40960 in
[Fri Jan  2 22:26:28 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:26:28 2026] ata4: hard resetting link
[Fri Jan  2 22:26:28 2026] ata4: SATA link down (SStatus 0 SControl 310)
[Fri Jan  2 22:26:28 2026] ata4: hard resetting link
[Fri Jan  2 22:26:33 2026] ata4: link is slow to respond, please be patient (ready=0)
[Fri Jan  2 22:26:38 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:26:38 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:26:38 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:26:43 2026] ata4.00: qc timeout after 5000 msecs (cmd 0xec)
[Fri Jan  2 22:26:43 2026] ata4.00: failed to IDENTIFY (I/O error, err_mask=0x4)
[Fri Jan  2 22:26:43 2026] ata4.00: revalidation failed (errno=-5)
[Fri Jan  2 22:26:43 2026] ata4: hard resetting link
[Fri Jan  2 22:26:44 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:26:44 2026] ata4.00: configured for UDMA/33
[Fri Jan  2 22:26:44 2026] ata4: EH complete
[Fri Jan  2 22:26:45 2026] ata4.00: exception Emask 0x50 SAct 0x801080 SErr 0x60802 action 0x6 frozen
[Fri Jan  2 22:26:45 2026] ata4.00: irq_stat 0x08000000, interface fatal error
[Fri Jan  2 22:26:45 2026] ata4: SError: { RecovComm HostInt PHYInt CommWake }
[Fri Jan  2 22:26:45 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:26:45 2026] ata4.00: cmd 60/50:38:18:df:c5/00:00:a8:01:00/40 tag 7 ncq dma 40960 in
[Fri Jan  2 22:26:45 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:26:45 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:26:45 2026] ata4.00: cmd 60/58:60:98:a0:33/00:00:a9:01:00/40 tag 12 ncq dma 45056 in
[Fri Jan  2 22:26:45 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:26:45 2026] ata4.00: failed command: READ FPDMA QUEUED
[Fri Jan  2 22:26:45 2026] ata4.00: cmd 60/58:b8:a0:e5:b9/00:00:1b:00:00/40 tag 23 ncq dma 45056 in
[Fri Jan  2 22:26:45 2026] ata4.00: status: { DRDY }
[Fri Jan  2 22:26:45 2026] ata4: hard resetting link
[Fri Jan  2 22:26:45 2026] ata4: SATA link down (SStatus 0 SControl 310)
[Fri Jan  2 22:26:45 2026] ata4: hard resetting link
[Fri Jan  2 22:26:50 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:26:50 2026] ata4: SATA link down (SStatus 0 SControl 310)
[Fri Jan  2 22:26:51 2026] ata4: hard resetting link
[Fri Jan  2 22:26:56 2026] ata4: link is slow to respond, please be patient (ready=0)
[Fri Jan  2 22:27:01 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:27:01 2026] ata4: found unknown device (class 0)
[Fri Jan  2 22:27:01 2026] ata4: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
[Fri Jan  2 22:27:06 2026] ata4.00: qc timeout after 5000 msecs (cmd 0xec)
[Fri Jan  2 22:27:06 2026] ata4.00: failed to IDENTIFY (I/O error, err_mask=0x4)
[Fri Jan  2 22:27:06 2026] ata4.00: revalidation failed (errno=-5)
[Fri Jan  2 22:27:06 2026] ata4.00: disable device
[Fri Jan  2 22:27:07 2026] ata4: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[Fri Jan  2 22:27:07 2026] ata4.00: ATA-11: ST4000NT001-3M2101, EN01, max UDMA/133
[Fri Jan  2 22:27:07 2026] ata4.00: 7814037168 sectors, multi 16: LBA48 NCQ (depth 32), AA
[Fri Jan  2 22:27:07 2026] ata4.00: Features: NCQ-sndrcv
[Fri Jan  2 22:27:07 2026] ata4.00: configured for UDMA/133
[Fri Jan  2 22:27:07 2026] sd 3:0:0:0: [sdb] tag#7 Sense Key : Not Ready [current] 
[Fri Jan  2 22:27:07 2026] sd 3:0:0:0: [sdb] tag#7 Add. Sense: Logical unit not ready, hard reset required
[Fri Jan  2 22:27:07 2026] I/O error, dev sdb, sector 7126507288 op 0x0:(READ) flags 0x0 phys_seg 2 prio class 0
[Fri Jan  2 22:27:07 2026] sd 3:0:0:0: [sdb] tag#12 Sense Key : Not Ready [current] 
[Fri Jan  2 22:27:07 2026] sd 3:0:0:0: [sdb] tag#12 Add. Sense: Logical unit not ready, hard reset required
[Fri Jan  2 22:27:07 2026] I/O error, dev sdb, sector 7133700248 op 0x0:(READ) flags 0x0 phys_seg 3 prio class 0
[Fri Jan  2 22:27:07 2026] I/O error, dev sdb, sector 630388008 op 0x0:(READ) flags 0x0 phys_seg 3 prio class 0
[Fri Jan  2 22:27:07 2026] sd 3:0:0:0: [sdb] tag#23 Sense Key : Not Ready [current] 
[Fri Jan  2 22:27:07 2026] sd 3:0:0:0: [sdb] tag#23 Add. Sense: Logical unit not ready, hard reset required
[Fri Jan  2 22:27:07 2026] I/O error, dev sdb, sector 465167776 op 0x0:(READ) flags 0x0 phys_seg 3 prio class 0
[Fri Jan  2 22:27:07 2026] I/O error, dev sdb, sector 2576 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[Fri Jan  2 22:27:07 2026] I/O error, dev sdb, sector 1847276792 op 0x0:(READ) flags 0x0 phys_seg 14 prio class 0
[Fri Jan  2 22:27:07 2026] I/O error, dev sdb, sector 7814018064 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[Fri Jan  2 22:27:07 2026] ata4: EH complete
[Fri Jan  2 22:27:07 2026] ata4.00: detaching (SCSI 3:0:0:0)
[Fri Jan  2 22:27:07 2026] I/O error, dev sdb, sector 1847277304 op 0x0:(READ) flags 0x0 phys_seg 3 prio class 0
[Fri Jan  2 22:28:39 2026] r8169 0000:07:00.0 eno1: Link is Down
[Fri Jan  2 22:28:42 2026] r8169 0000:07:00.0 eno1: Link is Up - 1Gbps/Full - flow control off

Outputs of suggested smartctl command:

SMART overall-health self-assessment test result: PASSED
Error logging capability:        (0x01)	Error logging supported.
  5 Reallocated_Sector_Ct   PO--CK   100   100   010    -    0
197 Current_Pending_Sector  -O--C-   100   100   000    -    0
198 Offline_Uncorrectable   ----C-   100   100   000    -    0
199 UDMA_CRC_Error_Count    -OSRCK   200   200   000    -    0
0x01           SL  R/O      1  Summary SMART error log
0x02           SL  R/O      5  Comprehensive SMART error log
0x03       GPL     R/O      5  Ext. Comprehensive SMART error log
0x0c       GPL     R/O   2048  Pending Defects log
0x10       GPL     R/O      1  NCQ Command Error log
0x11       GPL     R/O      1  SATA Phy Event Counters log
0x21       GPL     R/O      1  Write stream error log
0x22       GPL     R/O      1  Read stream error log
SMART Extended Comprehensive Error Log Version: 1 (5 sectors)
If Selective self-test is pending on power-up, resume after 0 minute delay.
0x03  0x020  4               0  ---  Number of Reallocated Logical Sectors
0x06  0x008  4              39  ---  Number of Hardware Resets
0x06  0x018  4               0  ---  Number of Interface CRC Errors
Pending Defects log (GP Log 0x0c)
SATA Phy Event Counters (GP Log 0x11)
0x000a  2            2  Device-to-host register FISes sent due to a COMRESET
0x0001  2            0  Command failed due to ICRC error

Turning off the disk:

Ran sudo zpool offline proxmox-tank-1 "$DISKID".

Once finished, status read:

  pool: proxmox-tank-1
state: DEGRADED
status: One or more devices is currently being resilvered.  The pool will
  continue to function, possibly in a degraded state.
action: Wait for the resilver to complete.
  scan: resilver in progress since Fri Jan  2 22:25:31 2026
  1.04T / 1.26T scanned at 1.14G/s, 96.2G / 523G issued at 106M/s
  0B resilvered, 18.41% done, no estimated completion time
config:

  NAME                                 STATE     READ WRITE CKSUM
  proxmox-tank-1                       DEGRADED     0     0     0
    mirror-0                           DEGRADED     0     0     0
      ata-ST4000NT001-3M2101_WX11TN0Z  OFFLINE    108   639   129
      ata-ST4000NT001-3M2101_WX11TN2P  ONLINE       0     0     0

Reseating
- I opened up the case. Generally it looked as if everything was properly seated. I revied the power and data ports on the disk, the power connection to the PSU tread and the data connection to the motherboard. Perhaps the faulty disk power port might have been sliiiiiightly loose, but not that much. All pins were clearly contacting. To be honest, it didn't look like it wasn't properly seated.
- In any case, I reaseted both of the connectors on the disk, and also the motherboard data one.
Booting again
- Is the disk detected?
  - ls -l /dev/disk/by-id/ | grep WX11TN0Z shows the disk is using sdb.
  - readlink -f "$DISKPATH" agrees.
- First check of dmesg shows the disk succesfully detected and attached as a SCSI drive. No more logs.

Adding the disk back to the pool

I add the disk back with sudo zpool online proxmox-tank-1 "$DISKID"

First status right after

  pool: proxmox-tank-1
state: DEGRADED
status: One or more devices is currently being resilvered.  The pool will
  continue to function, possibly in a degraded state.
action: Wait for the resilver to complete.
  scan: resilver in progress since Fri Jan  2 23:17:35 2026
  759G / 1.26T scanned at 8.43G/s, 0B / 618G issued
  0B resilvered, 0.00% done, no estimated completion time
config:

  NAME                                 STATE     READ WRITE CKSUM
  proxmox-tank-1                       DEGRADED     0     0     0
    mirror-0                           DEGRADED     0     0     0
      ata-ST4000NT001-3M2101_WX11TN0Z  DEGRADED     0     0     0  too many errors
      ata-ST4000NT001-3M2101_WX11TN2P  ONLINE       0     0     0

errors: No known data errors

It shows degraded, but 0 errors. I guess that's good news.
Printing multiple times shows the resilvering process is ongoing and progressing. I'll let that run for a while.
The writing part of the resilvering begins and the disk still shows 0 errors in the ZFS status. The kernel logs are quiet. The resilvering will take a while: the lagging disk must catch up on 524Gb of content. Dear god, for how long was that disk faulty???
The writing side of the resilvering is running at ~50MB/s. I'll shut down all the VMs in hopes of preventing contention for the disk IO.
After around 30min, speed has increased to 100MB/s.
The resilvering will take a long time and it's late, so I'l go to sleep and continue tomorrow.

The next morning, status read this:

  pool: proxmox-tank-1
state: DEGRADED
status: One or more devices has experienced an unrecoverable error.  An
  attempt was made to correct the error.  Applications are unaffected.
action: Determine if the device needs to be replaced, and clear the errors
  using 'zpool clear' or replace the device with 'zpool replace'.
  see: https://openzfs.github.io/openzfs-docs/msg/ZFS-8000-9P
  scan: resilvered 495G in 01:07:58 with 0 errors on Sat Jan  3 00:25:33 2026
config:

  NAME                                 STATE     READ WRITE CKSUM
  proxmox-tank-1                       DEGRADED     0     0     0
    mirror-0                           DEGRADED     0     0     0
      ata-ST4000NT001-3M2101_WX11TN0Z  DEGRADED     0     0     0  too many errors
      ata-ST4000NT001-3M2101_WX11TN2P  ONLINE       0     0     0

errors: No known data errors

Apparently, after a little crisis like the one this disk had, ZFS will only mark it clear with human acknowledgement.
To do that, I run: zpool clear proxmox-tank-1 ata-ST4000NT001-3M2101_WX11TN0Z

Status immediately becomes:

  pool: proxmox-tank-1
state: ONLINE
  scan: resilvered 495G in 01:07:58 with 0 errors on Sat Jan  3 00:25:33 2026
config:

  NAME                                 STATE     READ WRITE CKSUM
  proxmox-tank-1                       ONLINE       0     0     0
    mirror-0                           ONLINE       0     0     0
      ata-ST4000NT001-3M2101_WX11TN0Z  ONLINE       0     0     0
      ata-ST4000NT001-3M2101_WX11TN2P  ONLINE       0     0     0

errors: No known data errors

Scrubbing

I trigger the scrub with: sudo zpool scrub proxmox-tank-1

This is the final message once the scrub finished:

  pool: proxmox-tank-1
state: ONLINE
status: One or more devices has experienced an unrecoverable error.  An
  attempt was made to correct the error.  Applications are unaffected.
action: Determine if the device needs to be replaced, and clear the errors
  using 'zpool clear' or replace the device with 'zpool replace'.
  see: https://openzfs.github.io/openzfs-docs/msg/ZFS-8000-9P
  scan: scrub repaired 13.0M in 02:14:22 with 0 errors on Sat Jan  3 11:03:54 2026
config:

  NAME                                 STATE     READ WRITE CKSUM
  proxmox-tank-1                       ONLINE       0     0     0
    mirror-0                           ONLINE       0     0     0
      ata-ST4000NT001-3M2101_WX11TN0Z  ONLINE       0     0   992
      ata-ST4000NT001-3M2101_WX11TN2P  ONLINE       0     0     0

errors: No known data errors

I clear the error messages with zpool clear proxmox-tank-1 ata-ST4000NT001-3M2101_WX11TN0Z
Nevertheless, those checksum errors might be of concern.

Checking disk with smartctl

I run

smartctl -x "$(readlink -f "$DISKPATH")" | egrep -i 'Reallocated|Pending|Offline_Uncorrect|CRC|Hardware Resets|COMRESET|SATA Phy'

and get back:

  5 Reallocated_Sector_Ct   PO--CK   100   100   010    -    0
197 Current_Pending_Sector  -O--C-   100   100   000    -    0
198 Offline_Uncorrectable   ----C-   100   100   000    -    0
199 UDMA_CRC_Error_Count    -OSRCK   200   200   000    -    0
0x0c       GPL     R/O   2048  Pending Defects log
0x11       GPL     R/O      1  SATA Phy Event Counters log
If Selective self-test is pending on power-up, resume after 0 minute delay.
0x03  0x020  4               0  ---  Number of Reallocated Logical Sectors
0x06  0x008  4              41  ---  Number of Hardware Resets
0x06  0x018  4               0  ---  Number of Interface CRC Errors
Pending Defects log (GP Log 0x0c)
SATA Phy Event Counters (GP Log 0x11)
0x000a  2            2  Device-to-host register FISes sent due to a COMRESET
0x0001  2            0  Command failed due to ICRC error

The full output of smartctl -x /dev/sdb:

smartctl 7.4 2024-10-15 r5620 [x86_64-linux-6.14.8-2-pve] (local build)
Copyright (C) 2002-23, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Device Model:     ST4000NT001-3M2101
Serial Number:    WX11TN0Z
LU WWN Device Id: 5 000c50 0fb8869af
Firmware Version: EN01
User Capacity:    4,000,787,030,016 bytes [4.00 TB]
Sector Sizes:     512 bytes logical, 4096 bytes physical
Rotation Rate:    7200 rpm
Form Factor:      3.5 inches
Device is:        Not in smartctl database 7.3/5528
ATA Version is:   ACS-4 (minor revision not indicated)
SATA Version is:  SATA 3.3, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Sat Jan  3 11:16:38 2026 CET
SMART support is: Available - device has SMART capability.
SMART support is: Enabled
AAM feature is:   Unavailable
APM feature is:   Unavailable
Rd look-ahead is: Enabled
Write cache is:   Enabled
DSN feature is:   Disabled
ATA Security is:  Disabled, NOT FROZEN [SEC1]
Write SCT (Get) Feature Control Command failed: scsi error unsupported field in scsi command
Wt Cache Reorder: Unknown (SCT Feature Control command failed)

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x82)	Offline data collection activity
          was completed without error.
          Auto Offline Data Collection: Enabled.
Self-test execution status:      (   0)	The previous self-test routine completed
          without error or no self-test has ever 
          been run.
Total time to complete Offline 
data collection: 		(  567) seconds.
Offline data collection
capabilities: 			 (0x7b) SMART execute Offline immediate.
          Auto Offline data collection on/off support.
          Suspend Offline collection upon new
          command.
          Offline surface scan supported.
          Self-test supported.
          Conveyance Self-test supported.
          Selective Self-test supported.
SMART capabilities:            (0x0003)	Saves SMART data before entering
          power-saving mode.
          Supports SMART auto save timer.
Error logging capability:        (0x01)	Error logging supported.
          General Purpose Logging supported.
Short self-test routine 
recommended polling time: 	 (   1) minutes.
Extended self-test routine
recommended polling time: 	 ( 372) minutes.
Conveyance self-test routine
recommended polling time: 	 (   2) minutes.
SCT capabilities: 	       (0x50bd)	SCT Status supported.
          SCT Error Recovery Control supported.
          SCT Feature Control supported.
          SCT Data Table supported.

SMART Attributes Data Structure revision number: 10
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAGS    VALUE WORST THRESH FAIL RAW_VALUE
  1 Raw_Read_Error_Rate     POSR--   080   064   044    -    89842680
  3 Spin_Up_Time            PO----   097   093   000    -    0
  4 Start_Stop_Count        -O--CK   100   100   020    -    237
  5 Reallocated_Sector_Ct   PO--CK   100   100   010    -    0
  7 Seek_Error_Rate         POSR--   078   060   045    -    58464314
  9 Power_On_Hours          -O--CK   099   099   000    -    1551
10 Spin_Retry_Count        PO--C-   100   100   097    -    0
12 Power_Cycle_Count       -O--CK   100   100   020    -    237
18 Unknown_Attribute       PO-R--   100   100   050    -    0
187 Reported_Uncorrect      -O--CK   100   100   000    -    0
188 Command_Timeout         -O--CK   100   100   000    -    0
190 Airflow_Temperature_Cel -O---K   060   054   000    -    40 (Min/Max 26/43)
192 Power-Off_Retract_Count -O--CK   100   100   000    -    229
193 Load_Cycle_Count        -O--CK   100   100   000    -    1964
194 Temperature_Celsius     -O---K   040   046   000    -    40 (0 23 0 0 0)
197 Current_Pending_Sector  -O--C-   100   100   000    -    0
198 Offline_Uncorrectable   ----C-   100   100   000    -    0
199 UDMA_CRC_Error_Count    -OSRCK   200   200   000    -    0
240 Head_Flying_Hours       ------   100   100   000    -    516 (189 160 0)
241 Total_LBAs_Written      ------   100   253   000    -    19110016931
242 Total_LBAs_Read         ------   100   253   000    -    9057450849
                            ||||||_ K auto-keep
                            |||||__ C event count
                            ||||___ R error rate
                            |||____ S speed/performance
                            ||_____ O updated online
                            |______ P prefailure warning

General Purpose Log Directory Version 1
SMART           Log Directory Version 1 [multi-sector log support]
Address    Access  R/W   Size  Description
0x00       GPL,SL  R/O      1  Log Directory
0x01           SL  R/O      1  Summary SMART error log
0x02           SL  R/O      5  Comprehensive SMART error log
0x03       GPL     R/O      5  Ext. Comprehensive SMART error log
0x04       GPL     R/O    256  Device Statistics log
0x04       SL      R/O      8  Device Statistics log
0x06           SL  R/O      1  SMART self-test log
0x07       GPL     R/O      1  Extended self-test log
0x08       GPL     R/O      2  Power Conditions log
0x09           SL  R/W      1  Selective self-test log
0x0a       GPL     R/W      8  Device Statistics Notification
0x0c       GPL     R/O   2048  Pending Defects log
0x10       GPL     R/O      1  NCQ Command Error log
0x11       GPL     R/O      1  SATA Phy Event Counters log
0x13       GPL     R/O      1  SATA NCQ Send and Receive log
0x21       GPL     R/O      1  Write stream error log
0x22       GPL     R/O      1  Read stream error log
0x24       GPL     R/O    768  Current Device Internal Status Data log
0x2f       GPL     R/O      1  Set Sector Configuration
0x30       GPL,SL  R/O      9  IDENTIFY DEVICE data log
0x80-0x9f  GPL,SL  R/W     16  Host vendor specific log
0xa1       GPL,SL  VS     160  Device vendor specific log
0xa2       GPL     VS   16320  Device vendor specific log
0xa4       GPL,SL  VS     160  Device vendor specific log
0xa6       GPL     VS     192  Device vendor specific log
0xa8-0xa9  GPL,SL  VS     136  Device vendor specific log
0xab       GPL     VS       1  Device vendor specific log
0xad       GPL     VS      16  Device vendor specific log
0xb1       GPL,SL  VS     160  Device vendor specific log
0xb6       GPL     VS    1920  Device vendor specific log
0xbe-0xbf  GPL     VS   65535  Device vendor specific log
0xc1       GPL,SL  VS       8  Device vendor specific log
0xc3       GPL,SL  VS      24  Device vendor specific log
0xc6       GPL     VS    5184  Device vendor specific log
0xc7       GPL,SL  VS       8  Device vendor specific log
0xc9       GPL,SL  VS       8  Device vendor specific log
0xca       GPL,SL  VS      16  Device vendor specific log
0xcd       GPL,SL  VS       1  Device vendor specific log
0xce       GPL     VS       1  Device vendor specific log
0xcf       GPL     VS     512  Device vendor specific log
0xd1       GPL     VS     656  Device vendor specific log
0xd2       GPL     VS   10256  Device vendor specific log
0xd4       GPL     VS    2048  Device vendor specific log
0xda       GPL,SL  VS       1  Device vendor specific log
0xe0       GPL,SL  R/W      1  SCT Command/Status
0xe1       GPL,SL  R/W      1  SCT Data Transfer

SMART Extended Comprehensive Error Log Version: 1 (5 sectors)
No Errors Logged

SMART Extended Self-test Log Version: 1 (1 sectors)
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed without error       00%      1462         -

SMART Selective self-test log data structure revision number 1
SPAN  MIN_LBA  MAX_LBA  CURRENT_TEST_STATUS
    1        0        0  Not_testing
    2        0        0  Not_testing
    3        0        0  Not_testing
    4        0        0  Not_testing
    5        0        0  Not_testing
Selective self-test flags (0x0):
  After scanning selected spans, do NOT read-scan remainder of disk.
If Selective self-test is pending on power-up, resume after 0 minute delay.

SCT Status Version:                  3
SCT Version (vendor specific):       522 (0x020a)
Device State:                        Active (0)
Current Temperature:                    40 Celsius
Power Cycle Min/Max Temperature:     26/43 Celsius
Lifetime    Min/Max Temperature:     23/46 Celsius
Under/Over Temperature Limit Count:   0/2
SMART Status:                        0xc24f (PASSED)
Vendor specific:
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00

SCT Temperature History Version:     2
Temperature Sampling Period:         4 minutes
Temperature Logging Interval:        59 minutes
Min/Max recommended Temperature:     10/40 Celsius
Min/Max Temperature Limit:            5/60 Celsius
Temperature History Size (Index):    128 (123)

Index    Estimated Time   Temperature Celsius
124    2025-12-29 05:52    34  ***************
125    2025-12-29 06:51    34  ***************
126    2025-12-29 07:50    33  **************
...    ..(  3 skipped).    ..  **************
  2    2025-12-29 11:46    33  **************
  3    2025-12-29 12:45    35  ****************
  4    2025-12-29 13:44    35  ****************
  5    2025-12-29 14:43    35  ****************
  6    2025-12-29 15:42     ?  -
  7    2025-12-29 16:41    36  *****************
  8    2025-12-29 17:40     ?  -
  9    2025-12-29 18:39    36  *****************
  10    2025-12-29 19:38     ?  -
  11    2025-12-29 20:37    36  *****************
  12    2025-12-29 21:36    36  *****************
  13    2025-12-29 22:35    35  ****************
...    ..(  4 skipped).    ..  ****************
  18    2025-12-30 03:30    35  ****************
  19    2025-12-30 04:29    34  ***************
...    ..(  2 skipped).    ..  ***************
  22    2025-12-30 07:26    34  ***************
  23    2025-12-30 08:25    33  **************
  24    2025-12-30 09:24    33  **************
  25    2025-12-30 10:23    33  **************
  26    2025-12-30 11:22    32  *************
...    ..(  3 skipped).    ..  *************
  30    2025-12-30 15:18    32  *************
  31    2025-12-30 16:17    33  **************
  32    2025-12-30 17:16    33  **************
  33    2025-12-30 18:15    32  *************
...    ..( 10 skipped).    ..  *************
  44    2025-12-31 05:04    32  *************
  45    2025-12-31 06:03    31  ************
...    ..(  5 skipped).    ..  ************
  51    2025-12-31 11:57    31  ************
  52    2025-12-31 12:56    30  ***********
...    ..(  8 skipped).    ..  ***********
  61    2025-12-31 21:47    30  ***********
  62    2025-12-31 22:46    31  ************
...    ..(  3 skipped).    ..  ************
  66    2026-01-01 02:42    31  ************
  67    2026-01-01 03:41    30  ***********
...    ..( 10 skipped).    ..  ***********
  78    2026-01-01 14:30    30  ***********
  79    2026-01-01 15:29    29  **********
  80    2026-01-01 16:28    29  **********
  81    2026-01-01 17:27    29  **********
  82    2026-01-01 18:26    30  ***********
  83    2026-01-01 19:25    29  **********
  84    2026-01-01 20:24    29  **********
  85    2026-01-01 21:23    29  **********
  86    2026-01-01 22:22    30  ***********
  87    2026-01-01 23:21    30  ***********
  88    2026-01-02 00:20    32  *************
  89    2026-01-02 01:19    33  **************
  90    2026-01-02 02:18    33  **************
  91    2026-01-02 03:17    33  **************
  92    2026-01-02 04:16    32  *************
  93    2026-01-02 05:15    31  ************
  94    2026-01-02 06:14     ?  -
  95    2026-01-02 07:13    30  ***********
  96    2026-01-02 08:12     ?  -
  97    2026-01-02 09:11    30  ***********
  98    2026-01-02 10:10     ?  -
  99    2026-01-02 11:09    30  ***********
100    2026-01-02 12:08     ?  -
101    2026-01-02 13:07    30  ***********
102    2026-01-02 14:06     ?  -
103    2026-01-02 15:05    30  ***********
104    2026-01-02 16:04     ?  -
105    2026-01-02 17:03    30  ***********
106    2026-01-02 18:02     ?  -
107    2026-01-02 19:01    31  ************
108    2026-01-02 20:00     ?  -
109    2026-01-02 20:59    31  ************
110    2026-01-02 21:58     ?  -
111    2026-01-02 22:57    26  *******
112    2026-01-02 23:56    38  *******************
113    2026-01-03 00:55    36  *****************
114    2026-01-03 01:54    34  ***************
115    2026-01-03 02:53    33  **************
...    ..(  4 skipped).    ..  **************
120    2026-01-03 07:48    33  **************
121    2026-01-03 08:47    37  ******************
122    2026-01-03 09:46    42  ***********************
123    2026-01-03 10:45    43  ************************

SCT Error Recovery Control:
          Read:     70 (7.0 seconds)
          Write:     70 (7.0 seconds)

Device Statistics (GP Log 0x04)
Page  Offset Size        Value Flags Description
0x01  =====  =               =  ===  == General Statistics (rev 1) ==
0x01  0x008  4             237  ---  Lifetime Power-On Resets
0x01  0x010  4            1551  ---  Power-on Hours
0x01  0x018  6     18855234811  ---  Logical Sectors Written
0x01  0x020  6        38962968  ---  Number of Write Commands
0x01  0x028  6      9004753896  ---  Logical Sectors Read
0x01  0x030  6       148517033  ---  Number of Read Commands
0x01  0x038  6               -  ---  Date and Time TimeStamp
0x03  =====  =               =  ===  == Rotating Media Statistics (rev 1) ==
0x03  0x008  4            1203  ---  Spindle Motor Power-on Hours
0x03  0x010  4             516  ---  Head Flying Hours
0x03  0x018  4            1964  ---  Head Load Events
0x03  0x020  4               0  ---  Number of Reallocated Logical Sectors
0x03  0x028  4               0  ---  Read Recovery Attempts
0x03  0x030  4               0  ---  Number of Mechanical Start Failures
0x03  0x038  4               0  ---  Number of Realloc. Candidate Logical Sectors
0x03  0x040  4             229  ---  Number of High Priority Unload Events
0x04  =====  =               =  ===  == General Errors Statistics (rev 1) ==
0x04  0x008  4               0  ---  Number of Reported Uncorrectable Errors
0x04  0x010  4               0  ---  Resets Between Cmd Acceptance and Completion
0x04  0x018  4               0  -D-  Physical Element Status Changed
0x05  =====  =               =  ===  == Temperature Statistics (rev 1) ==
0x05  0x008  1              40  ---  Current Temperature
0x05  0x010  1              32  ---  Average Short Term Temperature
0x05  0x018  1              34  ---  Average Long Term Temperature
0x05  0x020  1              46  ---  Highest Temperature
0x05  0x028  1              27  ---  Lowest Temperature
0x05  0x030  1              43  ---  Highest Average Short Term Temperature
0x05  0x038  1              30  ---  Lowest Average Short Term Temperature
0x05  0x040  1              34  ---  Highest Average Long Term Temperature
0x05  0x048  1              34  ---  Lowest Average Long Term Temperature
0x05  0x050  4               0  ---  Time in Over-Temperature
0x05  0x058  1              60  ---  Specified Maximum Operating Temperature
0x05  0x060  4               0  ---  Time in Under-Temperature
0x05  0x068  1               5  ---  Specified Minimum Operating Temperature
0x06  =====  =               =  ===  == Transport Statistics (rev 1) ==
0x06  0x008  4              41  ---  Number of Hardware Resets
0x06  0x010  4               8  ---  Number of ASR Events
0x06  0x018  4               0  ---  Number of Interface CRC Errors
0xff  =====  =               =  ===  == Vendor Specific Statistics (rev 1) ==
0xff  0x010  7               0  ---  Vendor Specific
0xff  0x018  7               0  ---  Vendor Specific
                                |||_ C monitored condition met
                                ||__ D supports DSN
                                |___ N normalized value

Pending Defects log (GP Log 0x0c)
No Defects Logged

SATA Phy Event Counters (GP Log 0x11)
ID      Size     Value  Description
0x000a  2            2  Device-to-host register FISes sent due to a COMRESET
0x0001  2            0  Command failed due to ICRC error
0x0003  2            0  R_ERR response for device-to-host data FIS
0x0004  2            0  R_ERR response for host-to-device data FIS
0x0006  2            0  R_ERR response for device-to-host non-data FIS
0x0007  2            0  R_ERR response for host-to-device non-data FIS

Seagate FARM log (GP Log 0xa6) supported [try: -l farm]

smartctl -l error shows no errors.

smartctl -l selftest after triggering the short test:

smartctl 7.4 2024-10-15 r5620 [x86_64-linux-6.14.8-2-pve] (local build)
Copyright (C) 2002-23, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF READ SMART DATA SECTION ===
SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed without error       00%      1551         -
# 2  Short offline       Completed without error       00%      1462         -

Then I run the longtest. It will be finished at 18:00.
While the test runs, I start raising the host VMs again since they can run in parallel.
The selftest is taking way longer than initially planned, but it's progressing. It's 21:00, 20% remaining.

It finished eventually. Here's the full output:

smartctl 7.4 2024-10-15 r5620 [x86_64-linux-6.14.8-2-pve] (local build)
Copyright (C) 2002-23, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Device Model:     ST4000NT001-3M2101
Serial Number:    WX11TN0Z
LU WWN Device Id: 5 000c50 0fb8869af
Firmware Version: EN01
User Capacity:    4,000,787,030,016 bytes [4.00 TB]
Sector Sizes:     512 bytes logical, 4096 bytes physical
Rotation Rate:    7200 rpm
Form Factor:      3.5 inches
Device is:        Not in smartctl database 7.3/5528
ATA Version is:   ACS-4 (minor revision not indicated)
SATA Version is:  SATA 3.3, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Sat Jan  3 23:48:15 2026 CET
SMART support is: Available - device has SMART capability.
SMART support is: Enabled
AAM feature is:   Unavailable
APM feature is:   Unavailable
Rd look-ahead is: Enabled
Write cache is:   Enabled
DSN feature is:   Disabled
ATA Security is:  Disabled, NOT FROZEN [SEC1]
Write SCT (Get) Feature Control Command failed: scsi error unsupported field in scsi command
Wt Cache Reorder: Unknown (SCT Feature Control command failed)

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x82)	Offline data collection activity
          was completed without error.
          Auto Offline Data Collection: Enabled.
Self-test execution status:      (   0)	The previous self-test routine completed
          without error or no self-test has ever 
          been run.
Total time to complete Offline 
data collection: 		(  567) seconds.
Offline data collection
capabilities: 			 (0x7b) SMART execute Offline immediate.
          Auto Offline data collection on/off support.
          Suspend Offline collection upon new
          command.
          Offline surface scan supported.
          Self-test supported.
          Conveyance Self-test supported.
          Selective Self-test supported.
SMART capabilities:            (0x0003)	Saves SMART data before entering
          power-saving mode.
          Supports SMART auto save timer.
Error logging capability:        (0x01)	Error logging supported.
          General Purpose Logging supported.
Short self-test routine 
recommended polling time: 	 (   1) minutes.
Extended self-test routine
recommended polling time: 	 ( 372) minutes.
Conveyance self-test routine
recommended polling time: 	 (   2) minutes.
SCT capabilities: 	       (0x50bd)	SCT Status supported.
          SCT Error Recovery Control supported.
          SCT Feature Control supported.
          SCT Data Table supported.

SMART Attributes Data Structure revision number: 10
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAGS    VALUE WORST THRESH FAIL RAW_VALUE
  1 Raw_Read_Error_Rate     POSR--   082   064   044    -    160614704
  3 Spin_Up_Time            PO----   097   093   000    -    0
  4 Start_Stop_Count        -O--CK   100   100   020    -    237
  5 Reallocated_Sector_Ct   PO--CK   100   100   010    -    0
  7 Seek_Error_Rate         POSR--   078   060   045    -    63053692
  9 Power_On_Hours          -O--CK   099   099   000    -    1564
10 Spin_Retry_Count        PO--C-   100   100   097    -    0
12 Power_Cycle_Count       -O--CK   100   100   020    -    237
18 Unknown_Attribute       PO-R--   100   100   050    -    0
187 Reported_Uncorrect      -O--CK   100   100   000    -    0
188 Command_Timeout         -O--CK   100   100   000    -    0
190 Airflow_Temperature_Cel -O---K   063   054   000    -    37 (Min/Max 26/45)
192 Power-Off_Retract_Count -O--CK   100   100   000    -    229
193 Load_Cycle_Count        -O--CK   100   100   000    -    1965
194 Temperature_Celsius     -O---K   037   046   000    -    37 (0 23 0 0 0)
197 Current_Pending_Sector  -O--C-   100   100   000    -    0
198 Offline_Uncorrectable   ----C-   100   100   000    -    0
199 UDMA_CRC_Error_Count    -OSRCK   200   200   000    -    0
240 Head_Flying_Hours       ------   100   100   000    -    529 (206 38 0)
241 Total_LBAs_Written      ------   100   253   000    -    19648189091
242 Total_LBAs_Read         ------   100   253   000    -    9322473897
                            ||||||_ K auto-keep
                            |||||__ C event count
                            ||||___ R error rate
                            |||____ S speed/performance
                            ||_____ O updated online
                            |______ P prefailure warning

General Purpose Log Directory Version 1
SMART           Log Directory Version 1 [multi-sector log support]
Address    Access  R/W   Size  Description
0x00       GPL,SL  R/O      1  Log Directory
0x01           SL  R/O      1  Summary SMART error log
0x02           SL  R/O      5  Comprehensive SMART error log
0x03       GPL     R/O      5  Ext. Comprehensive SMART error log
0x04       GPL     R/O    256  Device Statistics log
0x04       SL      R/O      8  Device Statistics log
0x06           SL  R/O      1  SMART self-test log
0x07       GPL     R/O      1  Extended self-test log
0x08       GPL     R/O      2  Power Conditions log
0x09           SL  R/W      1  Selective self-test log
0x0a       GPL     R/W      8  Device Statistics Notification
0x0c       GPL     R/O   2048  Pending Defects log
0x10       GPL     R/O      1  NCQ Command Error log
0x11       GPL     R/O      1  SATA Phy Event Counters log
0x13       GPL     R/O      1  SATA NCQ Send and Receive log
0x21       GPL     R/O      1  Write stream error log
0x22       GPL     R/O      1  Read stream error log
0x24       GPL     R/O    768  Current Device Internal Status Data log
0x2f       GPL     R/O      1  Set Sector Configuration
0x30       GPL,SL  R/O      9  IDENTIFY DEVICE data log
0x80-0x9f  GPL,SL  R/W     16  Host vendor specific log
0xa1       GPL,SL  VS     160  Device vendor specific log
0xa2       GPL     VS   16320  Device vendor specific log
0xa4       GPL,SL  VS     160  Device vendor specific log
0xa6       GPL     VS     192  Device vendor specific log
0xa8-0xa9  GPL,SL  VS     136  Device vendor specific log
0xab       GPL     VS       1  Device vendor specific log
0xad       GPL     VS      16  Device vendor specific log
0xb1       GPL,SL  VS     160  Device vendor specific log
0xb6       GPL     VS    1920  Device vendor specific log
0xbe-0xbf  GPL     VS   65535  Device vendor specific log
0xc1       GPL,SL  VS       8  Device vendor specific log
0xc3       GPL,SL  VS      24  Device vendor specific log
0xc6       GPL     VS    5184  Device vendor specific log
0xc7       GPL,SL  VS       8  Device vendor specific log
0xc9       GPL,SL  VS       8  Device vendor specific log
0xca       GPL,SL  VS      16  Device vendor specific log
0xcd       GPL,SL  VS       1  Device vendor specific log
0xce       GPL     VS       1  Device vendor specific log
0xcf       GPL     VS     512  Device vendor specific log
0xd1       GPL     VS     656  Device vendor specific log
0xd2       GPL     VS   10256  Device vendor specific log
0xd4       GPL     VS    2048  Device vendor specific log
0xda       GPL,SL  VS       1  Device vendor specific log
0xe0       GPL,SL  R/W      1  SCT Command/Status
0xe1       GPL,SL  R/W      1  SCT Data Transfer

SMART Extended Comprehensive Error Log Version: 1 (5 sectors)
No Errors Logged

SMART Extended Self-test Log Version: 1 (1 sectors)
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Extended offline    Completed without error       00%      1563         -
# 2  Short offline       Completed without error       00%      1551         -
# 3  Short offline       Completed without error       00%      1462         -

SMART Selective self-test log data structure revision number 1
SPAN  MIN_LBA  MAX_LBA  CURRENT_TEST_STATUS
    1        0        0  Not_testing
    2        0        0  Not_testing
    3        0        0  Not_testing
    4        0        0  Not_testing
    5        0        0  Not_testing
Selective self-test flags (0x0):
  After scanning selected spans, do NOT read-scan remainder of disk.
If Selective self-test is pending on power-up, resume after 0 minute delay.

SCT Status Version:                  3
SCT Version (vendor specific):       522 (0x020a)
Device State:                        Active (0)
Current Temperature:                    37 Celsius
Power Cycle Min/Max Temperature:     26/45 Celsius
Lifetime    Min/Max Temperature:     23/46 Celsius
Under/Over Temperature Limit Count:   0/14
SMART Status:                        0xc24f (PASSED)
Vendor specific:
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00

SCT Temperature History Version:     2
Temperature Sampling Period:         4 minutes
Temperature Logging Interval:        59 minutes
Min/Max recommended Temperature:     10/40 Celsius
Min/Max Temperature Limit:            5/60 Celsius
Temperature History Size (Index):    128 (8)

Index    Estimated Time   Temperature Celsius
  9    2025-12-29 18:39    36  *****************
  10    2025-12-29 19:38     ?  -
  11    2025-12-29 20:37    36  *****************
  12    2025-12-29 21:36    36  *****************
  13    2025-12-29 22:35    35  ****************
...    ..(  4 skipped).    ..  ****************
  18    2025-12-30 03:30    35  ****************
  19    2025-12-30 04:29    34  ***************
...    ..(  2 skipped).    ..  ***************
  22    2025-12-30 07:26    34  ***************
  23    2025-12-30 08:25    33  **************
  24    2025-12-30 09:24    33  **************
  25    2025-12-30 10:23    33  **************
  26    2025-12-30 11:22    32  *************
...    ..(  3 skipped).    ..  *************
  30    2025-12-30 15:18    32  *************
  31    2025-12-30 16:17    33  **************
  32    2025-12-30 17:16    33  **************
  33    2025-12-30 18:15    32  *************
...    ..( 10 skipped).    ..  *************
  44    2025-12-31 05:04    32  *************
  45    2025-12-31 06:03    31  ************
...    ..(  5 skipped).    ..  ************
  51    2025-12-31 11:57    31  ************
  52    2025-12-31 12:56    30  ***********
...    ..(  8 skipped).    ..  ***********
  61    2025-12-31 21:47    30  ***********
  62    2025-12-31 22:46    31  ************
...    ..(  3 skipped).    ..  ************
  66    2026-01-01 02:42    31  ************
  67    2026-01-01 03:41    30  ***********
...    ..( 10 skipped).    ..  ***********
  78    2026-01-01 14:30    30  ***********
  79    2026-01-01 15:29    29  **********
  80    2026-01-01 16:28    29  **********
  81    2026-01-01 17:27    29  **********
  82    2026-01-01 18:26    30  ***********
  83    2026-01-01 19:25    29  **********
  84    2026-01-01 20:24    29  **********
  85    2026-01-01 21:23    29  **********
  86    2026-01-01 22:22    30  ***********
  87    2026-01-01 23:21    30  ***********
  88    2026-01-02 00:20    32  *************
  89    2026-01-02 01:19    33  **************
  90    2026-01-02 02:18    33  **************
  91    2026-01-02 03:17    33  **************
  92    2026-01-02 04:16    32  *************
  93    2026-01-02 05:15    31  ************
  94    2026-01-02 06:14     ?  -
  95    2026-01-02 07:13    30  ***********
  96    2026-01-02 08:12     ?  -
  97    2026-01-02 09:11    30  ***********
  98    2026-01-02 10:10     ?  -
  99    2026-01-02 11:09    30  ***********
100    2026-01-02 12:08     ?  -
101    2026-01-02 13:07    30  ***********
102    2026-01-02 14:06     ?  -
103    2026-01-02 15:05    30  ***********
104    2026-01-02 16:04     ?  -
105    2026-01-02 17:03    30  ***********
106    2026-01-02 18:02     ?  -
107    2026-01-02 19:01    31  ************
108    2026-01-02 20:00     ?  -
109    2026-01-02 20:59    31  ************
110    2026-01-02 21:58     ?  -
111    2026-01-02 22:57    26  *******
112    2026-01-02 23:56    38  *******************
113    2026-01-03 00:55    36  *****************
114    2026-01-03 01:54    34  ***************
115    2026-01-03 02:53    33  **************
...    ..(  4 skipped).    ..  **************
120    2026-01-03 07:48    33  **************
121    2026-01-03 08:47    37  ******************
122    2026-01-03 09:46    42  ***********************
123    2026-01-03 10:45    43  ************************
124    2026-01-03 11:44    42  ***********************
125    2026-01-03 12:43    43  ************************
126    2026-01-03 13:42    44  *************************
127    2026-01-03 14:41    45  **************************
  0    2026-01-03 15:40    43  ************************
  1    2026-01-03 16:39    43  ************************
  2    2026-01-03 17:38    42  ***********************
...    ..(  2 skipped).    ..  ***********************
  5    2026-01-03 20:35    42  ***********************
  6    2026-01-03 21:34    41  **********************
  7    2026-01-03 22:33    41  **********************
  8    2026-01-03 23:32    38  *******************

SCT Error Recovery Control:
          Read:     70 (7.0 seconds)
          Write:     70 (7.0 seconds)

Device Statistics (GP Log 0x04)
Page  Offset Size        Value Flags Description
0x01  =====  =               =  ===  == General Statistics (rev 1) ==
0x01  0x008  4             237  ---  Lifetime Power-On Resets
0x01  0x010  4            1564  ---  Power-on Hours
0x01  0x018  6     19393406971  ---  Logical Sectors Written
0x01  0x020  6        40248649  ---  Number of Write Commands
0x01  0x028  6      9269776944  ---  Logical Sectors Read
0x01  0x030  6       154066717  ---  Number of Read Commands
0x01  0x038  6               -  ---  Date and Time TimeStamp
0x03  =====  =               =  ===  == Rotating Media Statistics (rev 1) ==
0x03  0x008  4            1215  ---  Spindle Motor Power-on Hours
0x03  0x010  4             528  ---  Head Flying Hours
0x03  0x018  4            1965  ---  Head Load Events
0x03  0x020  4               0  ---  Number of Reallocated Logical Sectors
0x03  0x028  4               0  ---  Read Recovery Attempts
0x03  0x030  4               0  ---  Number of Mechanical Start Failures
0x03  0x038  4               0  ---  Number of Realloc. Candidate Logical Sectors
0x03  0x040  4             229  ---  Number of High Priority Unload Events
0x04  =====  =               =  ===  == General Errors Statistics (rev 1) ==
0x04  0x008  4               0  ---  Number of Reported Uncorrectable Errors
0x04  0x010  4               0  ---  Resets Between Cmd Acceptance and Completion
0x04  0x018  4               0  -D-  Physical Element Status Changed
0x05  =====  =               =  ===  == Temperature Statistics (rev 1) ==
0x05  0x008  1              37  ---  Current Temperature
0x05  0x010  1              35  ---  Average Short Term Temperature
0x05  0x018  1              34  ---  Average Long Term Temperature
0x05  0x020  1              46  ---  Highest Temperature
0x05  0x028  1              27  ---  Lowest Temperature
0x05  0x030  1              43  ---  Highest Average Short Term Temperature
0x05  0x038  1              30  ---  Lowest Average Short Term Temperature
0x05  0x040  1              34  ---  Highest Average Long Term Temperature
0x05  0x048  1              34  ---  Lowest Average Long Term Temperature
0x05  0x050  4               0  ---  Time in Over-Temperature
0x05  0x058  1              60  ---  Specified Maximum Operating Temperature
0x05  0x060  4               0  ---  Time in Under-Temperature
0x05  0x068  1               5  ---  Specified Minimum Operating Temperature
0x06  =====  =               =  ===  == Transport Statistics (rev 1) ==
0x06  0x008  4              41  ---  Number of Hardware Resets
0x06  0x010  4               8  ---  Number of ASR Events
0x06  0x018  4               0  ---  Number of Interface CRC Errors
0xff  =====  =               =  ===  == Vendor Specific Statistics (rev 1) ==
0xff  0x010  7               0  ---  Vendor Specific
0xff  0x018  7               0  ---  Vendor Specific
                                |||_ C monitored condition met
                                ||__ D supports DSN
                                |___ N normalized value

Pending Defects log (GP Log 0x0c)
No Defects Logged

SATA Phy Event Counters (GP Log 0x11)
ID      Size     Value  Description
0x000a  2            2  Device-to-host register FISes sent due to a COMRESET
0x0001  2            0  Command failed due to ICRC error
0x0003  2            0  R_ERR response for device-to-host data FIS
0x0004  2            0  R_ERR response for host-to-device data FIS
0x0006  2            0  R_ERR response for device-to-host non-data FIS
0x0007  2            0  R_ERR response for host-to-device non-data FIS

Seagate FARM log (GP Log 0xa6) supported [try: -l farm]

Execution finished, nothing else to do. The disk remains in the mirror.
Other notes
- I labeled the two disks by hand as AGAPITO1 and AGAPITO2, but I never noted their serial numbers. Silly me. This is the relation:
  - AGAPITO1 is ata-ST4000NT001-3M2101_WX11TN0Z.
  - AGAPITO2 is ata-ST4000NT001-3M2101_WX11TN2P.

Side quests

Using and understanding dmesg

Generalities

The Linux Kernel writes into the kernel ring buffer. This is an in-memory log where the kernel writes messages. The dmesg command reads from it. This log contains relatively low-level info from the kernel, including hardware related operations.

This is an in-memory structure because it starts very early in the boot process, right after the bootloader. Hence, information is held in-memory before the disk file-systems are available and syslog can persist logs.

Because of the in-memory nature, info on hardware failures is available in the kernel ring buffer before appearing in other persisted logs.

Good keywords to grep the output of dmesg to find hard drive related issues include:

ata
sata
ahci
link
COMRESET
PHY

Specific examples

Some examples of telling log lines:

ata4: hard resetting link
ata4: SATA link down (SStatus 0 SControl 300)
ata4: link is slow to respond, please be patient (ready=0)
ata4: found unknown device (class 0)

The disk is connecting and disconnecting, or appears slow, or doesn't display info for not being properly connected (unknown device).

ata4: limiting SATA link speed to 3.0 Gbps
ata4: limiting SATA link speed to 1.5 Gbps

Speed downgrades.

I/O error, dev sdb, sector 5414318144 op 0x0:(READ)
I/O error, dev sdb, sector 7814018064 op 0x0:(READ)

Failures of read attempts.

Why is it called dmesg?

dmesg stands for "diagnostic message".

What about persistence of logs?

Once userspace is available, systemd-journald reads messages. The kernel exposes the messages in /dev/kmsg for streaming. Those are copied into the in-memory journal. Then they get flushed to disk according to journald own policies and events.

Kernel messages have log levels (EMERG, ALERT, CRIT, ...). The userspace processes decide which levels deserve to hit disk persistence and what's simply left in the ring buffer.

Why do SATA drives get mentioned as SCIS drives in Kernel log messages?

SCIS is the protocol used by SAS drives.

The Linux Kernel uses the SCIS protocol as an emulated middleware layer between the actual ATA protocol used by the hard drive firmware.

Understanding smartctl

Naming and maintenance

Stands for Self-monitoring, Analysis, and Reporting Technology Control.

It's maintained by three randos, classic xkcd fragile software supply chain meme.

About the commands

smartctl -t short /dev/sdx prompts the drive to run a self-test. It's a very basic check that doesn't actually fully examine the disk. Having a failure in the short test basically guarantees that the disk is toast. It checks:

That CPU, RAM, etc work.
That the onboard microcode execution works fine.
It reads a small subset of the disk and verifies that it's readable.
It moves the mechanical parts to check they work.

By contrast, the longcheck (smartctl -t long /dev/sdx) actually reads every block on the disk to verify it can be read correctly.

smartctl -l selftest /dev/sdx just reads the result of the selftests.

On SATA vs SCSI (SAS) drives

SAS drives are enterprise drives with much more advanced reporting features and a different approach to transparency.

SATA drives run the vendor firmware, which keeps most details private and doesn't share them with the Linux. The drive itself decies when to report failues back to smartmontools.

SAS drives, on the other hand, provides more transparency, informs of failures earlier, and doesn't try to simplify and "hide" issues.

In the context of ZFS, SCSI helps the ZFS runtime realise faster that the disk is hiccup-y and make the call of marking it degraded and relying on alternative disks. SATA drives do not "confess" issues that fast, so the ZFS runtime keeps trying to use them and facing issues, which makes reads/writes fail and performance go to shit until finally ZFS decides to mark it degraded.

SAS drives don't fit on SATA ports: to plug them into a regular motherboard, you need a SAS controller

Open questions

How can I automate the monitoring of the ZFS pool or the disks to avoid this issue happening silently again?

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