Followed the directions from: https://blog.frankleonhardt.com/2025/add-mirror-to-single-zfs-disk/ but I don’t want to lose the notes, so I’m copying what I did here.
Move all data off the 4TB ssd (ada1)
Run the gpart function to move bootcode over:
gpart destroy -F ada1 ;
gpart backup ada0 | gpart restore ada1 ;
gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 ada1 ;Took the “ssd” zpool offline, and then attached as a mirror:
zpool destroy ssd;
zpool attach zroot ada0p4 ada1p4;Because the partition of the 1TB is not as large as the new 4TB drive, I waited until the resilvering completed, and then updated the end partition from 800GB -> 3.5TB.
gpart show ada1;
# Resize without a "size" flag takes all remaining space
gpart resize -i 4 ada1 ;
gpart show ada1;Now I need to sort out how to break the mirror and use only the 4TB disk.
Turns out efiboot is a royal pain and for some reason kept
referencing a device that didn’t exist in /etc/fstab when I
booted using the new drive.
To make edits to the root filesystem, I had to turn that on for ZFS:
zfs readonly=off zroot/ROOT/default
# Since we're here, let's make it autoexpand the pool
zpool set autoexpand=on zrootFor fstab, I had to change the values from:
# Device Mountpoint FStype Options Dump Pass#
/dev/gpt/efiboot0 /boot/efi msdosfs rw 2 2into:
# Device Mountpoint FStype Options Dump Pass#
/dev/ada0p1 /boot/efi msdosfs rw 2 2Once that was over, I was able to boot into a normal environment with all my usual stuff.
That lead to me seeing the (original sized) 800GB zfs root partition:
$ zpool list
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
archive 4.55T 2.44T 2.10T - - 0% 53% 1.00x ONLINE -
zroot 800G 29.8G 737G - ~2.7T 5% 9% 1.00x ONLINE -What?! I thought this was supposd to automatically grow the space!
zpool online -e zroot ada0p4 and then we have:
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
archive 4.55T 2.44T 2.10T - - 0% 53% 1.00x ONLINE -
zroot 3.51T 80.8G 3.43T - - 1% 2% 1.00x ONLINE -