Firstly - many thanks in advance for any suggestions!
I use a zfs mirror as my boot device (across several USB drives). This pool is called ‘freenas-boot’. I accidentally “added” a vdev into this pool, rather than replace an existing vdev with a new one. So I have ended up with the following config
nas-01# zpool status freenas-boot pool: freenas-boot state: ONLINE scan: resilvered 7.58G in 00:04:20 with 0 errors on Mon Nov 10 18:15:36 2025 config: NAME STATE READ WRITE CKSUM freenas-boot ONLINE 0 0 0 mirror-0 ONLINE 0 0 0 da2 ONLINE 0 0 0 da3 ONLINE 0 0 0 da0 ONLINE 0 0 0 da1 ONLINE 0 0 0
As you can see I’ve ended up with a single disk da1 as one vdev in the boot pool - not great! I don’t really know how to proceed and revert back to my 3-way mirror. I have tried “zpool remove” on da1 but unfortunately it has 4096 byte sectors and the mirror-0 has 512 byte sectors - so even though I can remove vdevs they don’t actually work. I realize I will likely need to migrate the boot pool to another pool but I don’t really understand how the boot system actually works such that the system comes up from that pool and am nervous of making matters worse.
What are your suggestions on next steps - my most likely is simply to add a mirror to da1 so that I retain redundancy on it.