Re: Advice configuring ServeRAID 8k for 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)