Can devices be removed from a ZFS pool?
Removal of a top-level vdev, such as an entire RAID-Z group or a disk in an unmirrored configuration, is not currently supported. This feature is planned for a future release. You can remove a device from a mirrored ZFS configuration by using the zpool detach command. You can replace a device with a device of equivalent size in both a mirrored or RAID-Z configuration by using the zpool replace command.