I am running a cache pool BTRFS Raid 1 for both data and metadata. 2 drives total, one of the drives is failing and I wanted to remove it from the cache pool.

https://docs.unraid.net/unraid-os/using-unraid-to/manage-storage/cache-pools/

I followed these steps:

To remove a disk using the WebGUI:

1. Stop the array: Go to the Main tab and look for the option to stop your array.

2. Unassign the pool drive: Find the drive you want to remove and unassign it in the Main tab.

3. Start the array: Restart the array to apply the changes.

4. Verify removal: Click on the first pool device in the Main tab, then check Balance Status (for BTRFS) or zpool status (for ZFS) to confirm the device was correctly removed.

Issue was when I got to step 3 after starting the array, the good cache pool drive shows "unmountable: wrong or no file system".

On unraid version 7.3.0.

ur1-diagnostics-20260525-0001.zip

The device is read-only, so Unraid will not be able to remove it from the pool. Try shutting down the server, physically removing that device, and then starting the array with the remaining one, if it still fails to mount, post new diags.