Re: RAID: Advantage or disaster?

Andy Kent <andykent.bristol.DontSpamMe_at_virgin.net> wrote:
>What do people think about the use of RAID for an IDS database these days?
>Better, worse, or about the same on balance as JABOD? Any RAID levels to
>prefer / avoid?
>
>A client of mine is running RAID 5 on Compaq, and is getting 100% disk i/o
>and frequent crashes. I haven't been able to look closely enough to
>establish whether it's the RAID 5 that's causing this, but anyway they're
>moving to a bigger box and planning to go RAID 5 again.
>
>Conventional wisdom and past experience tells me this would be a disaster.
>Has the technology moved on so as to tip the scales?

What are you trying to achieve with RAID - I/O bandwidth, reliability, or both?

If you need the I/O bandwidth then you really can't avoid RAID. If you need the reliability, likewise.

RAID 1+0 is wonderful, and solves most of your problems, but is expensive.

RAID 0 reduces the disk reliability but is great for performance. Don't use it unless you're willing to assume the risk.

RAID 5 is OK in its place. Traditionally it's been considered to be very poor for write performance but good for read, however I've recently seen very impressive results with striped RAID-5 sets (RAID 5+0 ?) behind a very large RAM cache (16 GB). I still wouldn't recommend it for redo logs though.

-- 
Andrew Mobbs - http://www.chiark.greenend.org.uk/~andrewm/