Is Raid 5 really that bad for Oracle?

I am quoting from Jonathan Lewis's book, Practical Oracle 8i, page 206

Raid 5 has an undeservedly bad reputation as far as Oracle database systems are concerned. ....
However, for most small systems, it is almost necessary and perfectly acceptable; and for many large systems it is totally adequate. ....
The first point is that many Oracle systems do far less writing than they do reading, and the writing is usually in the backgroud anyway, so although the write penalty is a notional 100%, this in=s not necessarily all that significant and overhead to the total I/O operation and many not impact the user directly anyway.

Second, although a single , small random write is likely to sustain a heavy penalty, RAID 5 suppliers are aware of the issue and have taken steps to reduce the problem. Typically a write that fills a whole stripe does not need to re-creates the parity as it writes each disk. It simply discards and re-creates a new parity block.

Third, it is beoming common practice to stick a reasonably large battery-backed cache on the Raid 5 device. Received on Sat Jul 31 2004 - 11:18:30 CDT