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ZFS Pool - Same drives in raidz2 and l2arc subpool

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After a view crashes of my system, caused by a faulty mainboard, I have an issue with my zfs pool.

Somehow, four of my raidz2 HDDs are also listed in the l2arc subpool.

Here is the output of zpool import:

pool: stronghold

id: 17308197520914921262

state: ONLINE

status: One or more devices were being resilvered.

action: The pool can be imported using its name or numeric identifier.

config:

stronghold ONLINE

raidz2-0 ONLINE

sdf1 ONLINE

sdg1 ONLINE

sdh1 ONLINE

sdj1 ONLINE

sdi1 ONLINE

sdk1 ONLINE

cache

sdf1

sdg1

sdh1

sdi1

sdb1

sdc1

sdd1

sde1

As you can see sdf1, sdg1, sdh1 and sdi1 are listed in the raidz2 and in the cache.

I can start the array and the filesystem is mounting the drives. All data is still appears to be there, but if i do a zpool status I get this:

pool: stronghold

state: ONLINE

status: One or more devices could not be used because the label is missing or

invalid. Sufficient replicas exist for the pool to continue

functioning in a degraded state.

action: Replace the device using 'zpool replace'.

see: https://openzfs.github.io/openzfs-docs/msg/ZFS-8000-4J

scan: scrub in progress since Sun Jun 1 05:00:01 2025

6.92T / 16.7T scanned at 10.2G/s, 90.3G / 16.7T issued at 133M/s

0B repaired, 0.53% done, 1 days 12:24:39 to go

config:

NAME STATE READ WRITE CKSUM

stronghold ONLINE 0 0 0

raidz2-0 ONLINE 0 0 0

sdf1 ONLINE 0 0 0

sdg1 ONLINE 0 0 0

sdh1 ONLINE 0 0 0

sdi1 ONLINE 0 0 0

sdj1 ONLINE 0 0 0

sdk1 ONLINE 0 0 0

cache

sdf1 FAULTED 0 0 0 corrupted data

sdg1 FAULTED 0 0 0 corrupted data

sdh1 FAULTED 0 0 0 corrupted data

sdi1 FAULTED 0 0 0 corrupted data

sdb1 ONLINE 0 0 0

sdc1 ONLINE 0 0 0

sdd1 ONLINE 0 0 0

sde1 ONLINE 0 0 0

errors: No known data errors

The scrub starts immediately, and I’m concerned that the resilvering might corrupt the data. I’m not sure if that risk is real.

I tried "zpool remove stronghold sdf1" but I got this error: cannot remove sdf1: operation not supported on this type of pool.

Then I tried deleting the pool and creating it again without the subpool, but after that the pool won't mount anymore: Unmountable: wrong or no file system

So I restored from a USB backup I created after my server crashed and the mainboard swap, but the duplicate drives were already there at that time.

Any guidance appreciated. 

tower-diagnostics-20250605-1103.zip

Edited by NoGames749
Diagnostics attached

Solved by JorgeB

  • Community Expert

You should always add the diags to a new post, or we won't see that the thread as new info, just saw it by chance, please post the output from:

zpool import -d /dev/disk/by-id

  • Author

I actually thought that might be the case, but didn't want to seem pushy by posting again, just to say that I attached it to my original post.

Anyway, thank you for your response, here’s the console output:

root@S1:~# zpool import -d /dev/disk/by-id

pool: light

id: 12952846355415526821

state: ONLINE

status: Some supported features are not enabled on the pool.

(Note that they may be intentionally disabled if the

'compatibility' property is set.)

action: The pool can be imported using its name or numeric identifier, though

some features will not be available without an explicit 'zpool upgrade'.

config:

light ONLINE

mirror-0 ONLINE

nvme-eui.0025384a21401ef6-part1 ONLINE

nvme-eui.0025384a2141525c-part1 ONLINE

mirror-1 ONLINE

nvme-eui.0025384a21401ecf-part1 ONLINE

nvme-eui.0025384a21401f2b-part1 ONLINE

pool: stronghold

id: 17308197520914921262

state: ONLINE

status: One or more devices were being resilvered.

action: The pool can be imported using its name or numeric identifier.

config:

stronghold ONLINE

raidz2-0 ONLINE

wwn-0x5000c500dc103c47-part1 ONLINE

wwn-0x5000c500dc109abd-part1 ONLINE

wwn-0x5000c500dc24a2c2-part1 ONLINE

wwn-0x5000c500db68a192-part1 ONLINE

wwn-0x5000c500db3fda93-part1 ONLINE

wwn-0x5000c500dc279672-part1 ONLINE

cache

sdf1

sdg1

sdh1

sdi1

wwn-0x5002538f42611244-part1

wwn-0x5002538f4261126a-part1

wwn-0x5002538f4261121c-part1

wwn-0x5002538f42611220-part1

  • Community Expert
  • Solution

With the array stopped, import the pool manually with that option:

zpool import -d /dev/disk/by-id stronghold

then type

zpool remove stronghold sdf1 sdg1 sdh1 sdi1

If that works, export the pool with zpool export stronghold then reimport with the GUI using the remaining devices:

on main click on the first device for that pool and then "remove pool"

back on main, create a new pool with the same name and 10 slots

assign the remaining pool devices all together, don't create subspools, leave the filesystem set to auto

start the array to import the pool, you should now be able to add the missing L2ARC devices again using the GUI.

  • Author

I tried the first steps and they worked. The pool is currently being exported again. Just to clarify: Why 10 slots? Am I including the cache devices? Because the RaidZ2 only had 6 devices.

  • Community Expert
11 minutes ago, NoGames749 said:

Am I including the cache devices? Because the RaidZ2 only had 6 devices.

You can include the remaining cache devices, unless you prefer to remove them all now, and then add them back later all together, that will also work.

  • Author

Everything is working normally again now.

A few more comments:

I created the pool with only the 6 HDDs from the vdev, meaning no cache. Then I started the array, but it didn't finish mounting.

I had to restart the server because I couldn't stop the array. After the restart, the cache was there with one slot:

Bildschirmfoto 2025-06-12_12-22-34 Jump Desktop-Dev-Simon-New.jpg

zpool import even showed me all 4 cache drives. I then set the slot to 0, and then I was able to start the array and the mounting was successful.

Maybe this will help the next person with the same issue.

Thank you so much for your help.

  • Community Expert
41 minutes ago, NoGames749 said:

zpool import even showed me all 4 cache drives.

So the pool imported without the L2ARC vdev, it shouldn't, can you post a new zpool status output?

  • Author
3 minutes ago, JorgeB said:

So the pool imported without the L2ARC vdev, it shouldn't, can you post a new zpool status output?

Everything I say here happened after this step:

7 hours ago, JorgeB said:

on main click on the first device for that pool and then "remove pool"

I recreated the pool without the L2ARC subpool, I started the array but the mounting wouldn't finish.
The zpool status output was:

root@S1:~# zpool status
  pool: stronghold
 state: ONLINE
status: Some supported and requested features are not enabled on the pool.
        The pool can still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
        the pool may no longer be accessible by software that does not support
        the features. See zpool-features(7) for details.
  scan: resilvered 637M in 7 days 14:58:59 with 0 errors on Thu Jun 12 01:50:56 2025
config:

        NAME                            STATE     READ WRITE CKSUM
        stronghold                      ONLINE       0     0     0
          raidz2-0                      ONLINE       0     0     0
            sdf1                        ONLINE       0     0     0
            sdg1                        ONLINE       0     0     0
            sdh1                        ONLINE       0     0     0
            sdi1                        ONLINE       0     0     0
            sdj1                        ONLINE       0     0     0
            sdk1                        ONLINE       0     0     0
        cache
          wwn-0x5002538f42611244-part1  ONLINE       0     0     0
          wwn-0x5002538f4261126a-part1  ONLINE       0     0     0
          wwn-0x5002538f4261121c-part1  ONLINE       0     0     0
          wwn-0x5002538f42611220-part1  ONLINE       0     0     0

errors: No known data errors

As you can see, the L2ARC cache is still there even though I didn't add it again.

I waited about an hour, so I had to reboot the server because I don't know of any way to stop the array while its "starting".

After rebooting, I was shown the cache with one slot and no drive assigned in the GUI, which is what the screenshot in my last post shows.

1 hour ago, NoGames749 said:

Bildschirmfoto 2025-06-12_12-22-34 Jump Desktop-Dev-Simon-New.jpg

First, I tried setting the slot count to 4, assigning my cache drives, and starting the array, but I got this error:

Wrong Pool State: cache - invalid config.

So I unassigned the cache drives and set the slot count to 0.

I started the array and it was mounted successfully.

zpool status was then:

root@S1:~# zpool status
  pool: stronghold
 state: ONLINE
status: Some supported and requested features are not enabled on the pool.
        The pool can still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
        the pool may no longer be accessible by software that does not support
        the features. See zpool-features(7) for details.
  scan: resilvered 637M in 7 days 14:58:59 with 0 errors on Thu Jun 12 01:50:56 2025
config:

        NAME        STATE     READ WRITE CKSUM
        stronghold  ONLINE       0     0     0
          raidz2-0  ONLINE       0     0     0
            sdf1    ONLINE       0     0     0
            sdg1    ONLINE       0     0     0
            sdh1    ONLINE       0     0     0
            sdi1    ONLINE       0     0     0
            sdj1    ONLINE       0     0     0
            sdk1    ONLINE       0     0     0

errors: No known data errors 

Then I stopped the array again, added a 4-slot L2ARC subpool with my drives, started the array, and the zpool status output now shows:

root@S1:~# zpool status
  pool: stronghold
 state: ONLINE
status: Some supported and requested features are not enabled on the pool.
        The pool can still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
        the pool may no longer be accessible by software that does not support
        the features. See zpool-features(7) for details.
  scan: resilvered 637M in 7 days 14:58:59 with 0 errors on Thu Jun 12 01:50:56 2025
config:

        NAME        STATE     READ WRITE CKSUM
        stronghold  ONLINE       0     0     0
          raidz2-0  ONLINE       0     0     0
            sdf1    ONLINE       0     0     0
            sdg1    ONLINE       0     0     0
            sdh1    ONLINE       0     0     0
            sdi1    ONLINE       0     0     0
            sdj1    ONLINE       0     0     0
            sdk1    ONLINE       0     0     0
        cache
          sdb1      ONLINE       0     0     0
          sdc1      ONLINE       0     0     0
          sdd1      ONLINE       0     0     0
          sde1      ONLINE       0     0     0

errors: No known data errors

Everything now works as I am used to.

Edited by NoGames749

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