Am 23.12.2011 08:05, schrieb Scott Marlowe:
On Thu, Dec 22, 2011 at 11:18 PM, tuanhoanganh<hatuan05@xxxxxxxxx> wrote:
Thanks for your answer. But how performance between raid5 and one disk.
One disk will usually win, 2 disks (in a mirror) will definitely win.
RAID-5 has the highest overhead and the poorest performance,
especially if it's degraded (1 drive out) that simple mirroring
methods don't suffer from. But even in an undegraded state it is
usually the slowest method. RAID-10 is generally the fastest with
redundancy, and of course pure RAID-0 is fastest of all but has no
redundancy.
You should do some simple benchmarks with something like pgbench and
various configs to see for yourself. For extra bonus points, break a
mirror (2 disk -> 1 disk) and compare it to RAID-5 (3 disk -> 2 disk
degraded) for performance. The change in performance for a RAID-1 to
single disk degraded situation is usually reads are half as fast and
writes are just as fast. For RAID-5 expect to see it drop by a lot.
I'm not so confident that a RAID-1 will win over a single disk. When it
comes to writes, the latency should be ~50 higher (if both disk must
sync), since the spindles are not running synchronously. This applies to
softraid, not something like a battery-backend raid controller of course.
Or am I wrong here?
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