I am a very new user to Unraid, only a few weeks since I started. I have been getting frustrated with my choice of such a small cache drive as it was initially intended just to be a boot drive. When I was setting my server up initially the installer suggested splitting the drive into the boot partition and then a data partition (which it named cache by default). I then learned later what the cache was and used it liberally, and have quickly seen the need for a larger drive. I bought a 2TB SATA SSD, and physically installed it tonight. I think this is when I made a series of mistakes. I shut down the array, changed the cache pool slots from 1 to 2, assigned the SSD to slot 2, then tried to start the array. I got an error saying flash 2 was missing identification, and then the system hung up never coming online. I had no option to shut down the array or restore it to its previous state. I panicked after some time and tried a reboot of the server (as that's typically the easiest way to solve things in the other contexts in life I interact with technology). Now the server boots and doesn't hang up, but I cannot start the array. Any time I try to do so I get a popup error saying

Wrong Pool State

cache - invalid expansion

and no matter what I do I can't seem to get the array back online. I found a few threads talking about this same error, and most of the solutions involved removing the pool and adding it again and the config imports and fixes itself. However, I don't seem to have that option for this pool! I'm assuming that's because it was set up as a partition on the boot drive. My only option is to erase the pool entirely, which is expressly described as deleting everything on the drives. This is obviously not ideal. Am I missing something obvious, or have I fucked up beyond repair due to ignorance and panicking?

Below is the initial error I received that was the start of the issues, then the alert that showed up after rebooting, and attached is my diagnostics. The Patriot drive is the drive I initially had installed as the boot drive, and the TEAMGROUP drive is the newly installed drive.

Event: Unraid Flash 2 error
Subject: Alert [J-SERVER] - Flash 2 in error state (disk dsbl)
Description: No device identification ()
Importance: alert

Event: Unraid pool status
Subject: Notice [J-SERVER] - Pool flash recovered to ONLINE
Description: Pool: flash (zfs) - Mountpoint: /boot
Importance: normal

j-server-diagnostics-20260720-2211.zip

Please post output from btrfs fi show

As requested

Label: none  uuid: 97c8c5c9-29d9-46ab-8bf4-9c585b24fa53
        Total devices 1 FS bytes used 34.05GiB
        devid    1 size 206.47GiB used 74.02GiB path /dev/nvme0n1p4

The boot pool is using both devices, but the data partition is only using one of them, if you are OK with formatting the data partition, it should be possible to start the array after clicking the 1st pool device and then "erase pool" (any data on the data partition would be lost), if there's data there, you would need to mount that filesystem manually, copy its data, then reformat.

If you need to mount the filesystem manually, this should work.

mkdir /x

mount -t btrfs /dev/nvme0n1p4 /x

You can then access the data under /x

Understood. Will give this a go in about 12 hours after work and report back. Thank you!

That did indeed do the trick. Annoying to have to copy back and forth and reformat, but that'll just teach me not to panic in the future and plan ahead and look up precise steps on how to do things. Thanks again!