We've had a couple Compaq/HP SANS here for our Demo system, 90 servers, all with no local storage, booting remotely off the SAN.
We just got a new SAN, 12TB, for production use, of which a piece will be databases. Liely still will keep the c: drive (OS and SQL) on local storage, the data and log files on the SAN. Not my choice, just the way winds are blowing here.
We had a big meeting with HP. The SAN has 160 drives, basically carved into 2 groups. Lots of work on how the 2 groups are striped, basically some variation of RAID 5, can lose 4 of the 80 drives before there's data loss. Remote mirroring across the campus, blah, blah.
Anyway, the recommendation for dbs was to place Server 1 data on disk group 1, Server 1 logs on disk group 2. Then for server 2 you reverse for some fault tolerance. In the event a disk group dies (notice they tout how fault tolerant this is, but they want you to have 2 groups. Interesting), haven't lost all yo' stuff.
So I'm not thrilled. I've got a heavy performance monster going here, about .5TB ad hoc reporting, and they want the logs on one group, data on another. Plus file servers are on the SAN.
What does that mean for performance? HP claims shouldn't be a big deal. So many spindles. OK, I buy that, but is some big honking machine with 80 spindles really more efficient for a DB than a few 15 spindle arrays? NetIQ mentioned efficiency is way down after 9-10 drives. Wouldn't it be better to have a bunch of 10 drive arrays that can be striped together?
Maybe that's what they do and don't tell us, but I'm not sold. I'll be happy to report some experiences once we get live on the new SAN. Course the server hardware is going form a 4x4 (550MHz) to a 4X8 (2GHz), so that will mask things. Hey, why take chances.
Plus it will make the SAN guys look good. I'm still curious to see if anyone is ever going to run the TPC marks against the same server hardware with local SCSI and on a SAN. Not sure anyone wants to see the numbers (including vendors). I'm just not thrilled with sharing db disks with file disks, but we'll see.
Steve Jones