Re: Best RAID Option FOr Oracle DB Files & Redo Logs

Jerry Gitomer <jgitomer_at_erols.com> wrote:

-> Playing the role of Devil's Advocate I say it depends on what you
-> mean by best. If your concern is performance then RAID0 (striping
-> without mirroring) is best. If your concern is capacity per dollar
-> then RAID5 is the best. If you want a compromise that will give you
-> most of the performance of RAID0 plus a safety net to protect against
-> hardware failure then and only then is RAID10 best.

I like RAID10. You get the performance of striping, plus the redundancy of mirroring. Unlike with RAID5, you can get a very high level of redundancy with the mirroring. For example, on a Sun Enterprise 4500 I can put the mirrors on separate controllers, which are on separate I/O boards. If a storage enclosure fails, if a controller fails, even if a complete I/O board files, I can order a part and hot swap it while the database is still online and in use. When adding drives too, with mirroring, I can create a new "device" with the desired size, sync it up with the existing mirrors, detach one of the existing mirrors, create another "device" of the desired size, sync it up to the existing mirrors, detach the other "small-old" mirror, then grow the new file system to the desired size. Plus, if I have a three-way mirror, I can detach a mirror and do a backup from the mirror, then sync it back up while I am done, with my database online during the backup.

Finally, there is a read performance benefit to having a mirror, as you can roundrobin amongst the mirrors for reads to spread the I/O load out.

Yeah, it takes at least double the disks, but if you have the bucks to do this, the increase in availability is good.

-- 
John Cronin