Justin Piszcz wrote:
On Mon, 13 Oct 2008, Bill Davidsen wrote:
Over a year ago I mentioned RAID-5e, a RAID-5 with the spare(s)
distributed over multiple drives. This has come up again, so I
thought I'd just mention why, and what advantages it offers.
By spreading the spare over multiple drives the head motion of normal
access is spread over one (or several) more drives. This reduces
seeks, improves performance, etc. The benefit reduces as the number
of drives in the array gets larger, obviously with four drives using
only three for normal operation is slower than four, etc. And by
using all the drives all the time, the chance of a spare being
undetected after going bad is reduced.
This becomes important as array drive counts shrink. Lower cost for
drives ($100/TB!), and attempts to drop power use by using fewer
drives, result in an overall drop in drive count, important in
serious applications.
All that said, I would really like to bring this up one more time,
even if the answer is "no interest."
--
Bill Davidsen <davidsen@xxxxxxx>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark
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Bill,
Not a bad idea; however, can the same not be acheived (somewhat) by
performing daily/smart, weekly/long tests on the drive to validate its
health? I find this to work fairly well on a large scale.
Not really, the performance benefit comes from spreading head motion to
(at least) one more drive. You can get a check on basic functionality
with SMART, but it doesn't beat the drive the way real load does. Add to
that the unfortunate problem that more realistic testing also takes up
i/o bandwidth for non-productive transfers. Better to be doing actual
live data transfers to those drives if you can.
--
Bill Davidsen <davidsen@xxxxxxx>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark
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