On Tue, 9 Dec 2014, Tim Hamilton <hamilton.tim@gmail.com> wrote:
If I was to follow your example, I could create 2 raidz1 vdevs of 3 drives each, 1 of these using the 3x3tb drives and 1 making use the other 3tb drive and my 2 biggest capacity old drives. This vdev would obviously be limited to the capacity by the smallest of these drives. I could then grow my storage pool when needed by upgrading the two older drives to match the larger 3tb. One downside would be that, for now, I wouldn't be making use of a big chunk of one of the 3tb drives. On the other hand, I don't yet have the data to fill it.
The other obvious path would be to simply use the 4x3tb drives in a raid5 pool managed by mdadm and forgo zfs filesystem features, though I did want to make use of snapshots.
Why not just use 4*3TB disks in a RAID-Z array? That gives you 9TB of usable space. 5TB disks are on sale now and aren't particularly expensive, if every time you have a problem with a 3TB disk you replace it with a 5TB disk (or 6TB when they become available) then you'll probably end up with a couple of 5+TB disks in a few years. ZFS SHOULD work over a mdadm RAID-0 array or a LVM volume that spans multiple physical disks. So if you find yourself with 2*3TB and 2*5TB disks in your array you could replace those 3TB disks with RAID-0 arrays that have 5TB capacity. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/