I'm working on datacenter upgrades now and am considering using RAID 6 instead of RAID 5 for a new mail server.

RAID 6 provides 2 parity drives, so any 2 drives can fail simultaneously without taking down the array/server. I used to run RAID 5 with a hot spare, so this is sort of like having a live hot-spare. With a 5-drive RAID 6 array, you get 3x the space of one drive and can take 2 hits.

Reports I read recently indicate that much more common is double drive failure in RAID 5, because the drives are now so large that it takes a long time to rebuild the array (sometimes 12-24 hrs!) and because during this time the other drives are so heavily taxed that a waring drive might fail during the rebuild of the array.

In addition, I have heard that while RAID 5 costs approx 7-12% write overhead, RAID 6 can cost 15-30% write overhead. Of course, reading has no overhead performance cost.

I'm wondering if anyone has used RAID 6 and can share their experience, specifically using a PERC 6/i w/ 256 MB RAID controller.

Thanks! Ken.