zpool list tank
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
tank 58.2T 22.0T 36.2T - - 8% 37% 1.00x ONLINE /mnt
zfs list tank
NAME USED AVAIL REFER MOUNTPOINT
tank 14.7T 7.78T 240K /mnt/tank
The used and available changed by about the space of the snapshots I deleted before I ran zfs rewrite -r /mnt/tank. The extends ran 12 hours each (had to do one at a time). The expand seemed almost immediate. The rewrite took close to 24 hours. No errors were reported by any of the above.
You can do a search for the RAID-Zx-expansion tag and read on space reporting. CLI should be more accurate than the GUI reporting but, I believe, it is still off. Backup data, recreate pool at full width and restore data is a recommendation if you want it to report better
Thank you, but I cannot backup and recreate the data without significant expense. I currently have no spare drives and no way to physically connect them to the server.
Can I somehow “unextend” the pool and at least get my two drives back?
I will now search the RAID-Zx-expansion tag as you suggested.
No, you cannot shrink a raidz vdev.
The added space is there to use, but reporting is botched. There is a pull request on OpenZFS to improve it but it may take time to review the PR.
