One of the frequently asked questions regarding ZFS. Is it possible to resize a RAIDZ, RAIDZ2 or MIRRORED ZPOOL?
The answer is a littlebit complicated…
If you want to change the ‘geometry’ of the ZPOOL (for example: change from a mirrored pool to a raidz, or simply add a disk to a raidz, or change from raidz to raidz2) then the answer is no.
But it is possible to change the disks of a pool with bigger ones and use the space.