Growing the Capacity of a ZFS Mirror
When I set up my OpenSolaris server, in order to save on money I had to skimp a little on the disks. I’m only at about 33% capacity right now, but once I pass the 50% mark it will be a good idea to start shopping around for larger disks. By then nice cheap 2TB or 3TB drives should be available. But there’s no reason I can’t get prepared now!
The process for growing a zpool is fairly straightforward.
- Attach new devices
- Wait for resilver
- Detach old devices
- Export/import pool (or reboot if operating on the root pool)
First, let’s get set up by creating some file vdevs for testing. Two 128MB to represent the old drives and two 256MB representing the new ones.
# mkfile 128m /vdev/v0 # mkfile 128m /vdev/v1 # mkfile 256m /vdev/v0 # mkfile 256m /vdev/v1 # ls -l /vdev -rw------- 1 root root 134217728 Apr 3 06:16 /vdev/v0 -rw------- 1 root root 134217728 Apr 3 06:17 /vdev/v1 -rw------- 1 root root 268435456 Apr 3 06:21 /vdev/x0 -rw------- 1 root root 268435456 Apr 3 06:21 /vdev/x1
Now I’ll create my play area, and check the size.
# zpool create play mirror /vdev/v0 /vdev/v1 # zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT play 123M 74.5K 123M 0% ONLINE -
Okay, 123MB. Next I’ll attach one of my larger vdevs and wait for it to resilver. Since I’m using empty files as stand-ins for disks they’ll resilver almost instantly. MAKE SURE YOU DO NOT DETACH A DISK BEFORE THE NEW DISK IS DONE RESILVERING. You will destroy your data.
# zpool attach play /vdev/v0 /vdev/x0 # zpool detach play /vdev/v0 # zpool attach play /vdev/v1 /vdev/x1 # zpool detach play /vdev/v1
With the new devices attached my pool still doesn’t look any different.
# zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT play 123M 74.5K 123M 0% ONLINE -
Until I re-import the pool.
# zpool export play # zpool import -d /vdev play # zpool list NAME SIZE USED AVAIL CAP HEALTH ALTROOT play 251M 91K 251M 0% ONLINE - #
Obviously you will need down time to perform this operation since you need to fully export the pool (or reboot the system if operating on the root pool).