As you mention, the SAN companies have combated the the issue with larger caches, and to my knowledge, my company solely uses RAID 5 in all SAN arrays. We differentiate tier 1 with tier 2 and tier 3 with the size of cache on the arrays and the RPM's of the disk. We consider our tier 1 to be EMC Symmetrix with 15k disks and the larger write cache. We have XP HP Arrays that have mixed disks.

Ultimately, from a DBA team perspective, for better or worse, our SAN configuration is a black hole because there are so many different arrays and brands in play (EMC Sym/ Clariion, NetApp, etc). We haven't seen very many problems with RAID 5 and that is what our SAN admins continually tell us is how they carve up the arrays.

They pre-provision the arrays when they are built, so it's difficult for us to even request a RAID 10 LUN from them because they simply "don't do it".

Best regards,

Steve