I understand that ZFS prefers to have as much data about the drives as possible, and that the best thing to do is turn off RAID.
The hardware environment is a Dell PowerEdge 2850 with PERC 4/DC and four drives (73Gb each) installed out of six possible. The software is FreeNAS 8.0.2 with ZFS booting from USB key.
I've configured the RAID this way: each physical drive is a logical drive in a RAID 0. No special configurations were made beyond this.
Is this optimal for ZFS? How do I properly set this up under FreeNAS as a ZRAID? Do I want to?
In my reading it was said that one can't add a new disk to a ZRAID pool; is this still true? How would you go about adding two new disks in a redundant fashion to a zpool in FreeNAS?
Answer
No, this is not optimal for ZFS. This is outlined at: ZFS SAS/SATA controller recommendations
The PERC 4/DC controller is a basic PCI-X parallel SCSI RAID controller. ZFS prefers to handle whole-disk management, so the better option in your case is to use a basic SCSI HBA. In lieu of that, the solution you've come up with by creating multiple RAID 0 logical drives will work. The only issue comes up when a drive fails. The replacement disk will need to be reinitialized as a RAID 0 logical drive in order to be recognized by ZFS. You will probably need a reboot in order to do this. It's something to consider.
Disk expansion is possible in certain cases. You can add vdevs (groupings of RAID disks) to a pool. For instance, if you have a zpool comprised of striped-mirrors (RAID 1+0), you can add additional mirrored pairs to that pool. You cannot expand a RAIDZ1/2/3 vdev.
Also see: ZFS: Mirror vs. RAID-Z and How can I add one disk to an existing raidz zpool?
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