Michael Shadle wrote:
On Mon, Apr 27, 2009 at 4:51 PM, Scott Lawson
<scott.law...@manukau.ac.nz> wrote:
If possible though you would be best to let the 3ware controller expose
the 16 disks as a JBOD to ZFS and create a RAIDZ2 within Solaris as you
will then
gain the full benefits of ZFS. Block self healing etc etc.
There isn't an issue in using a larger amount of disks in a RAIDZ2, just
that it
is not the optimal size. Longer rebuild times for larger vdev's in a zpool
(although this
is proportional to how full the pool is.). Two parity disks gives you
greater cover in
the event of a drive failing in a large vdev stripe.
Hmm, this is a bit disappointing to me. I would have dedicated only 2
disks out of 16 then to a single large raidz2 instead of two 8 disk
raidz2's (meaning 4 disks went to parity)
No I was referring to a single RAIDZ2 vdev of 16 disks in your pool. So
you would
lose ~2 disks to parity effectively. The larger the stripe, potentially
the slower the rebuild.
If you had multiple vdevs in a pool that were smaller stripes you would
get less performance
degradation by virtue of IO isolation. Of course here you lose pool
capacity. With
smaller vdevs, you could also potentially just use RAIDZ and not RAIDZ2
and then you would
have the equivalent size pool still with two parity disks. 1 per vdev.
One thing you haven't mentioned is the drive type and size that you are
planning to use as this
greatly influences what people here would recommend. RAIDZ2 is built for
big, slow SATA
disks as reconstruction times in large RAIDZ's and RAIDZ2's increase the
risk of vdev failure
significantly due to the time taken to resilver to a replacement drive.
Hot spares are your friend!
I was still operating under the impression that vdevs larger than 7-8
disks typically make baby Jesus nervous.
You did also state that this is a system to be used for backups? So
availability is five 9's?
Are you planning on using Open Solaris or mainstream Solaris 10?
Mainstream Solaris
10 is more conservative and is capable of being placed under a support
agreement if need
be.
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