On Mon, Jun 24, 2013 at 07:37:56PM +1000, Russell Coker wrote:
On Mon, 24 Jun 2013, Craig Sanders <cas@taz.net.au> wrote:
if you can, use the third SATA port for the RAID-Z array as well - RAID-Z gets better performance when the number of data disks in an array is a power of 2 (e.g. 4 data disks + 1 parity for RAID-Z1, or 4 data disks + 2 parity for RAID-Z2).
The SATA disks will just be for booting. They won't have ZFS because root on ZFS was way too much pain to even consider last time I looked into it. Also I think we are a long way from having ZFS root be reliable enough that I would even consider using it on a remote system with no other forms of boot available.
i made no mention of having root on ZFS. that's a completely unrelated topic.
I was pointing out that there is a small but noticable performance benefit with ZFS RAID-Z arrays if you have a power-of-two number of *data* disks - e.g. 2, 4, or 8 data disks.
with 5 SAS ports, you can have 4 data disk (yes, a power of 2) and 1 parity for RAID-Z1. Or you can have three data disks (NOT a power of 2) and 2 parity disks for RAID-Z3.
With old hardware like that I would nominate the 5th disk as a hot spare so on failure you have minimum "degraded" time. This assumes that ZFS can handle a hot spare drive. James