On Sep 30, 2009, at 6:03 PM, Matthew Ahrens wrote:
Erik Trimble wrote:
From a global perspective, multi-disk parity (e.g. raidz2 or
raidz3) is the way to go instead of hot spares.
Hot spares are useful for adding protection to a number of vdevs,
not a single vdev.
Even when using raidz2 or 3, it is useful to have hot spares so that
reconstruction can begin immediately. Otherwise it would have to
wait for the operator to physically remove the failed disk and
insert a new one.
When I model these things, I use 8 hours logistical response time for
data centers and 48 hours for SOHO. When the disks were small, and
thus resilver times were short, the logistical response time could make
a big impact. With 2+ TB drives, the resilver time is becoming dominant.
As disks becoming larger and not faster, there will be a day when the
logistical response time will become insignificant. In other words, you
won't need a spare to improve logistical response, but you can consider
using spares to extend logistical response time to months. To take this
argument to its limit, it is possible that in our lifetime RAID boxes
will
be disposable... the razor industry will be proud of us ;-)
-- richard
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