Q

Best RAID level for database

When designing a database, what is the best option for RAID level? We have RAID 5 and some think that we should have Raid 0+1. Personally, I hate using RAID 5 for database systems. And many, many top industry experts agree with me. Database systems are write-intensive creatures. Just to keep an Oracle database up and running and fulfilling requests, you need to have online redo logs, undo space, temporary sort space, not to mention...

write intensive operations (like INSERT, UPDATE, and DELETE statements) that hit your database's datafiles. So a database can generate lots of write requests. RAID 5 includes a write penalty caused by the method in which it calculates and stores parity bit information to be used in the event of a failure. So knowing that your database is most likely write intensive, why would you choose a RAID level that includes a write penalty? RAID 5 on write intensive datafiles will introduce a performance bottleneck. For that reason, I stay away from RAID 5 for databases unless I have very specific reasons to choose otherwise.

RAID 5 is very good for read operations though since the file is striped across multiple disk volumes. If your database is READ MOSTLY, then you may consider RAID 5, but that is rarely the case. RAID 0+1 does not have the write penalty like RAID 5 does. And RAID 0+1 also stripes the data so the read performance is as good as RAID 5. The only downside to RAID 0+1 is that you waste more physical disk space to set up the redundancy. But if I had my vote, it would go to RAID 0+1 every time over RAID 5.

This was first published in December 2003

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