RE: RAID 5 performance

4x is exactly what the theory says. Every write operation on a RAID 5 involves two reads - original block and checksum block, computes the new checksum and writes back new block and new checksum block - that makes 4 I/O operations. The only thing that can (not always) help is a write-back cache, but this can be VERY dangerous even with battery-backed caches.

What I have seen as a recomendation is either to avoid RAID5 or to put on it only datafiles that at not very much written and put the write intensive ones (redo logs, possibly temp and rollback) on RAID 1 or 1+0.

HTH a bit,

Dr. Nikolay Kumanov

MIS Manager, Zeitungsgruppe Bulgarien GmbH 47, Tsarigradsko chaussee, Sofia 1504, Bulgaria phone: +(359-2)4339-643, fax: +(359-2)946-1286 mailto:nkumanov_at_zgb.bg

"Show me a completely smooth operation and I'll show you someone who's covering mistakes. Real boats rock." - Frank Herbert, "Chapterhouse: Dune"

-----Original Message-----
From: Suhen Pather [mailto:Suhen.Pather_at_strandbags.com.au] Sent: Wednesday, January 24, 2001 6:06 AM To: Multiple recipients of list ORACLE-L Subject: RAID 5 performance
<<snip>>

Any write operation takes 4x longer on RAID 5 compared to a local disk on the PowerEdge 6450.
I am trying to tune/configure the hardware properly before I start on the Received on Wed Jan 24 2001 - 07:22:59 CST