Raid 5 vs 3

I am planning an Oracle installation for 2 applications. The first application is very write intensive at both the O/S and the database level. (bulk loads and processing of many millions of rows each night) The other application is more balanced in respect to reads and writes. (mostly OLTP stuff)

The bosses already shot down Raid 0+1 because of cost and (to be honest) what seems to be sheer prejudice.

So I'm evaluating Raid levels 3 and 5. I understand the basics behind these levels but I must be missing something.

If my information is correct then Raid 3 offers the highest transfer rates of all raid levels for both reading and writing. Furthermore it has the same fault tolerance as Raid 5 in that it can lose any single drive (even the parity drive) with minimal impact.

Raid 5 on the other hand seems to offer great read performance but suffers with write operations. It can survive a single drive failure with a slightly greater performance hit than with Raid 3.

Ok, if all this is true then why would ANYONE go with Raid 5? Raid 3 seems superior in all ways. What am I missing?

Thank you in advance,
Roger Westbrook
Dollar General Corp
rwestbrook_at_dollargeneral.com Received on Wed Jun 07 2000 - 00:00:00 CDT