I'd love to hear more discussion on RAID configuration for databases on a SAN. We have a few relatively new SQL Servers on a SAN here, and right now the whole SAN is RAID 5, and it's all configured as one big pool on the SAN side, and the sysadmins just carve chunks out of this one big pool whenever we need space. Our performance is good, but I'm pretty sure that's because we're always writing to the cache. In short, I'm not very comfortable without mirrored or RAID 10 storage for my logs and separate RAID 5 or RAID 10 for my data.

So I'd like to hear people's war stories regarding the following: what happens to our throughput if we get busy enough to flood the cache? And how hard is it to flood a SAN cache? Has this happened to any of you? I'm concerned, because the attitude here seems to be "when that happens, we'll just buy more." Is my paranoia level justified?

By the way, even if you give me great anecdotal and theoretical evidence that our configuration is terrible, I might not be able to do much about it. Everybody here seems to be enthralled with our SAN performance because it's better than the local storage they used to have, so I might be in a politics-trump-technology situation.

Any comments?