| From: | Matthew Wakeling <matthew(at)flymine(dot)org> |
|---|---|
| To: | Pierre C <lists(at)peufeu(dot)com> |
| Cc: | Kenneth Cox <kenstir(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Advice configuring ServeRAID 8k for performance |
| Date: | 2010-08-06 09:17:06 |
| Message-ID: | alpine.DEB.2.00.1008061013050.2654@aragorn.flymine.org |
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| Thread: | |
| Lists: | pgsql-performance |
On Thu, 5 Aug 2010, Scott Marlowe wrote:
> RAID6 is basically RAID5 with a hot spare already built into the
> array.
On Fri, 6 Aug 2010, Pierre C wrote:
> As others said, RAID6 is RAID5 + a hot spare.
No. RAID6 is NOT RAID5 plus a hot spare.
RAID5 uses a single parity datum (XOR) to ensure protection against data
loss if one drive fails.
RAID6 uses two different sets of parity (Reed-Solomon) to ensure
protection against data loss if two drives fail simultaneously.
If you have a RAID5 set with a hot spare, and you lose two drives, then
you have data loss. If the same happens to a RAID6 set, then there is no
data loss.
Matthew
--
And the lexer will say "Oh look, there's a null string. Oooh, there's
another. And another.", and will fall over spectacularly when it realises
there are actually rather a lot.
- Computer Science Lecturer (edited)
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