On Mon, 3 Aug 2009, Joachim Sandvik wrote:
We are looking at a dual cpu Supermicro server with about 32gb ram
and 2 x250gb OS disks, 21 x 1TB SATA disks, and 1 x 64gb SSD disk.
The system will use nexenta's auto-cdp which i think are based on
AVS to remote mirror to a system a few miles away. The system will
mostly be serving as a NFS server for our Vmware servers. We have
about 80 vm's who access the vmfs datastores.
I have read that its smart to use a few small raid groups in a
larger pools, but i am uncertain about placing 21 disks in 1pool.
21 disks in 1 pool should not be a problem.
The setup i have though of so far are:
1 pool with 3 x raidz2 groups with 6x1tb disks. 2x 64gb ssd for
cache and 2 spare disks. This should give us about 12TB
An another setup i have been thinking about is:
1 pool with 9 x mirror with 2 x 1TB, also with 2 spares and 2 64gb SSD.
Do anyone have a recommendation on what might be a good setup?
The mirror configuration will provide much better multiuser
performance (IOPS) since it offers so many more vdevs (9 vs 3) and the
vdevs are simple. The MTTDL is not quite as good as raidz2 but since
you are providing spare disks, and because resilver of a mirror disk
is fast, it should be quite reliable. If you do a periodic scrub of
the array, there should not be much concern about read errors during
resilver.
The mirror configuration will provide much better random read
performance than raidz2 since any drive in the mirror may be used to
return a read request (similar to 18 readable vdevs vs 3).
Usually when raidz2 is used, many more disks are used per vdev so that
it is more space efficient but in your case it is not that much more
space efficent than mirroring (12GB vs 9GB).
If 9GB is enough space for your needs, then it is likely that mirrors
are the best configuration. It is safer to err in the direction of
more performance since you can always add disk later if you need more
space, but adding performance is more expensive once the data is in
place.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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