Need help with pool configuration after adding disks

TrueNAS General
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1

Hi there,

I had done something stupid and am now stuck. Need help!

For a year, we ran TrueNAS Scale on 4x12Tb discs, and recently bought a dedicated server to run 10x12Tb with 6 new discs and 4 from the old NAS.

I installed TrueNAS Community Edition 25.04.2.1 on a new box with 6 HDDs and 3 SSDs for ZFS caches, copied data from the old drive to the new one, and checked the consistency of the data.

After that, I installed 4 HDDs from the old drive. TrueNAS displayed them as an array and suggested adding them to the existing pool (stupid me, I should have expanded the existing pool). So now I have a problem: Storage Dashboard->Topology->Data VDEVs shows 2 x Mixed Capacity and warning Mixed VDEV Capacities, Mixed VDEV Widths.

My pool consists of two RAIDZ1 arrays, one with 6 disks and one with 4. I cannot remove the second array from the pool, or release discs, or stop it somehow.

Is it possible to detach the second RAIDZ1 from the pool and add discs to the first one?

Any help here will be deeply appreciated.
-rth

P.S. I have no right to upload images, so I do my best to describe the problem
P.S.S. I have searched the forum, but couldn’t find anything; perhaps I used the wrong keywords.

2 
sudo zpool status -v
  pool: boot-pool
 state: ONLINE
config:

        NAME         STATE     READ WRITE CKSUM
        boot-pool    ONLINE       0     0     0
          nvme1n1p3  ONLINE       0     0     0

errors: No known data errors

  pool: root_data_storage
 state: ONLINE
  scan: resilvered 120K in 00:00:01 with 0 errors on Fri Aug 22 11:00:22 2025
config:

        NAME                                      STATE     READ WRITE CKSUM
        root_data_storage                         ONLINE       0     0     0
          raidz1-0                                ONLINE       0     0     0
            632f5f71-61a4-4939-9e1f-fefa1d6615aa  ONLINE       0     0     0
            f56af3b3-ca10-4b73-8ced-13a53c84bb35  ONLINE       0     0     0
            a2af57ff-b955-4dbc-bd10-efdb017feb0e  ONLINE       0     0     0
            904b312a-813c-4cef-bd13-d54e5a70b781  ONLINE       0     0     0
            5cf9a0f6-eeda-47b4-a2fa-332fa8182afd  ONLINE       0     0     0
            b81087f0-6dd2-4607-bccc-c714c5160690  ONLINE       0     0     0
          raidz1-1                                ONLINE       0     0     0
            360c40ef-deba-4d80-8c07-da2fd98188ad  ONLINE       0     0     0
            8208ba8b-d475-4147-adbd-27f5d6faa319  ONLINE       0     0     0
            ee58f03f-8798-4f0d-bee5-d46e28bfc199  ONLINE       0     0     0
            28fbf304-c7e4-424b-904d-46b0aabdf3fc  ONLINE       0     0     0
        cache
          ce35fa03-24f2-41ed-befe-2b8fabe16092    ONLINE       0     0     0
          89c7e26c-946b-4c0d-a0c8-573fef110864    ONLINE       0     0     0
          dbe8ad25-73a5-46ad-ac24-330ff5a5e099    ONLINE       0     0     0

errors: No known data errors
3

You can’t detach the second vdev. At this point to fix this, you take a full backup of your data - send / recv does great for this. Verify twice that you really have everything. Destroy the entire pool, and start from scratch.

4

Oh dear me! @yorick that isn’t possible. We don’t have 30+Tb additional storage for backup. So no way out of this. Can it work and be stable in this topology?

5

Ok so upon reading this again … yes you’re fine. They are both raidz1, which means you intended to have relatively low redundancy. The second vdev can be expanded to 6-wide at some point if you like.

Do take a backup. During resilver when you replace a drive there’s always an increased risk of a second drive failure, which your pool wouldn’t survive.

I wouldn’t go wider than 6-wide with these two vdevs. If you ever need much more storage, do another pool (not another vdev) with 8-wide raidz2 or 12-wide raidz3, maybe 22tb disks at that point. But that’s something you can ponder for the future.

For now you’re good because both vdevs have the same redundancy level.

Read the ZFS primer that ars published. It’ll help you with pool planning. One thing ZFS needs is careful planning. ZFS 101—Understanding ZFS storage and performance - Ars Technica

2 Likes
6

@yorick thank you so much!