Re: RAID 5 vs. RAID 0+1 vs. RAID 1+0

"Zeus" <Big_guy_at_gods.com> wrote in message news:<qK229.76665$v53.3506867_at_news3.calgary.shaw.ca>...
> I know Oracle recommends RAID 0+1 or 1+0 for OLTP systems (particularly for
> small, random writes) because of the RAID 5 write penalty. Does anyone have
> any direct experience or information on how big the difference is or how
> many concurrent users you'd need to have to make a significant difference?
>
> Also, what do people think of the 'SAME' (stripe and mirror everything)
> methodology where you mash everything together in the same stripe?
>
> TIA
If your entire disk farm for the database consists of 1 set of 5 disk on a raid-5 hardware device then I see no reason to have more than one stripe, but if you have a choice between 1 ten disk raid 5 stripe vs 2 five disk stripes I would go with two stripes. After all raid 5 only protects against the loss of 1 disk per stripe.

Given a choice I would go with OS level stripping and mirror at the disk level, which I think is 1+0 but I can never remember which is which 1+0, 0+1.

Believe it or not I am aware of a site that OS mirrows Raid 5 disk to a second Raid 5 box. Their overall performance is very good, but both Raid 5 units are behind large caches, which I think greatly helps hide the write twice penalty of Raid 5.

Sometimes as a DBA you just take what you given and do you best to spead your databases accross the available disk as best you can.

• Mark D Powell --