Follow-up to a very similar case I found (topic 200027) — same root symptom (device added without a partition, "Unmountable: no pool uuid" / "wrong or no file system"), but with an extra complication that thread didn't have.

Setup: single btrfs pool "multimedia" (2 devices: NVMe partition nvme0n1p4 + SATA SSD sdb, no separate parity array — this pool holds everything).

What I did (following the linked thread's guidance), successfully:

btrfs filesystem df confirmed Data/Metadata/System were RAID1 profile (despite fsProfile="single" in Unraid's own disks.ini — seems to just reflect intent, not live state).

btrfs balance start -mconvert=single -dconvert=single -sconvert=single -f /mnt/multimedia — completed cleanly, all profiles now single.

btrfs device remove /dev/sdb /mnt/multimedia — completed cleanly. btrfs filesystem show now reports Total devices 1, all ~619GiB intact on nvme0n1p4, no errors.

Where I'm stuck (unlike the linked thread):

The "multimedia" pool has bootPool="yes" in its live disks.ini state, and is displayed nested under the "Boot Pool" section in the Main GUI (alongside "Internal Boot", which itself shows DEGRADED — a separate zfs mirror boot pool missing its second device).

I believe this is because nvme0n1 (multimedia's device 1) is the same physical disk that also hosts the real boot pool's partition (nvme0n1p3, zfs, label "flash") — i.e., a shared disk, not an intentional "make this pool bootable" choice.

Because of this, DeviceInfo.page's $poolBootSizeLocked check (bootPool != "no") permanently disables the "Remove Pool" button for this pool.

With device 2 set to "no device" on Main, the pool shows Device 2: Kein Datenträger / Fehlend: Samsung_SSD_870_EVO..., and the "Slots" dropdown only offers "2" — can't reduce to 1. Starting the array in this state gives "Wrong Pool — multimedia — missing devices."

So I can't do the "remove pool, recreate with same name and 1 slot, reassign, filesystem auto" fix from the linked thread, because Remove Pool itself is locked.

Question: Given the pool's boot-pool linkage is (I believe) incidental to sharing a physical disk with the actual boot mirror, is there a supported way to either (a) safely clear/bypass this lock for a non-dedicated boot-linked pool, or (b) another path to get Unraid to re-recognize this now-single-device, verified-healthy pool without formatting? Data is 100% intact and currently mounted/serving fine manually via CLI as an interim measure. Diagnostics attached.

nas01-diagnostics-20260818-1316.zip

Right because you have a mirrored boot pool with your data partition you would have to remove the now missing device from BOTH filesystems (btrfs and zfs) before the whole 2nd disk can be removed and re-assigned.

Can you post the output of zpool status flash

Edit: I found it in the diags:

pool: flash
state: DEGRADED
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: resilvered 1.19G in 00:00:03 with 0 errors on Mon Aug 17 23:26:59 2026
config:
	NAME                      STATE     READ WRITE CKSUM
	flash                     DEGRADED     0     0     0
	  mirror-0                DEGRADED     0     0     0
	    nvme0n1p3             ONLINE       0     0     0
	    15148541010099398958  UNAVAIL      0     0     0  was /dev/sdb3
errors: No known data errors

Edited 7 hours ago7 hr by MowMdown

pool: flash

state: DEGRADED

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: resilvered 1.19G in 00:00:03 with 0 errors on Mon Aug 17 23:26:59 2026

config:

NAME STATE READ WRITE CKSUM

flash DEGRADED 0 0 0

mirror-0 DEGRADED 0 0 0

nvme0n1p3 ONLINE 0 0 0

15148541010099398958 UNAVAIL 0 0 0 was /dev/sdb3

errors: No known data errors

Please post the output of wipefs /dev/sdb

root@NAS01:~# wipefs /dev/sdb

root@NAS01:~#

can you post a screenshot of the MAIN page on your nas showing all the disks?

Try this:

Go to settings - Disk Settings and disable auto start

Open a terminal window and type

zpool detach flash 15148541010099398958

mv /boot/config/pools/multimedia.cfg /boot/config/pools/multimedia.bak

Reboot the server

Add a new pool named multimedia, 1 slot

Assign the NVMe device

Start array

The pool should be imported with the single device; it may initially show in the normal pool section, instead of the boot pool, but if that is the case, a reboot should move it there.

I do find it quite odd that device sdb isn't reporting any partitions.