On Sep 16, 2009, at 6:43 PM, Bob Friesenhahn <bfrie...@simple.dallas.tx.us
> wrote:
On Wed, 16 Sep 2009, Ross Walker wrote:
There is another type of failure that mirrors help with and that is
controller or path failures. If one side of a mirror set is on one
controller or path and the other on another then a failure of one
will not take down the set.
You can't get that with RAIDZn.
Sure you can. Just make sure that 'n' is the same as the number of
data disks, and make sure that each disk in the vdev is accessed via
a unique controller path. Use raidz3 with six disks. You probably
need a lot of vdevs to make this even somewhat cost effective. :-)
Well yes, if you have an equal number of parity disks to data disks it
would survive, but at that point what's the cost effectiveness to
resilency ratio?
Regardless, mirrors are known to be more resilient to temporary path
failures.
As another list member pointed out you could also avoid the issue by
having a raidz disk per controller. But if I'm buying that kind of big
iron I might just opt for a 3par or emc and save myself the work, and
probably some $ too.
-Ross
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