Re: RAID on Hitachi 9900 w/Oracle?

Nuno Souto wrote:
>
> Partly true. I don't know about the specific case of the Hitachi, but
> the EMC is similar and I know about that one. Their cache can really
> hide many of the disadvantages of RAID5 in a database.
>
> I still would go for RAID1+0 for the redo logs, but that's about it. The
> rest can happily live in RAID5 in those boxes.
>
> Of course, if you have a very unusual application with tremendous demands
> off the I/O system, then you may need to refine the concept and use all
> RAID1+0. But for 90% of the stuff out there, the default will do nice.
> IOW, it won't be where your performance problem (if any) will live.

Mostly I agree with the above, until a disk fails. Then you're talking about a fairly high amount of overhead to rebuild it, and a pretty long rebuild time with today's 73 or 140 GB disks (10, 12, 20+ hours depending on your load). The longer the rebuild time, the longer performance suffers, and the more you are exposed to the risk of a second disk failure in the RAID group causing data loss. Not sure about Hitachi, but in newer EMC Sym towers with large disks, EMC discourages the use of RAID5 due to the rebuild time and overhead costs.

Regards,
Sean M Received on Sat Aug 17 2002 - 11:18:16 CDT