August 29, 2008 at 8:36 am
We currently have our database on an HP EVA3000 configured as RAID 1 spread over 42 drives. The performance is good but and obvious issue is that usable capacity is about half of physical drive space.
We are talking to another SAN vendor, EqualLogic, which is a real advocate of RAID 50. They claim to have many customers using this configuration in a high-performance environment.
Has anyone had any eperience with RAID 50?
August 29, 2008 at 10:55 am
I have no experience with Raid 50, but personally I would recommend against it.
Raid 50 is striping multiple Raid 5's together. The claim by the SAN vendors is that it solves the Write problems that SQL Server (and other DBMS's) have with Raid 5, by expanding the effective bandwidth and by allowing for the possibility for the 2 read steps of the Raid 5 to be simultaneous (and also, possibly, if there are 2 write steps).
The thing is A) the "Raid 5 Write Problem" for DMBS's is primarily an effective service time problem, and not a throughput problem. Increased bandwidth is not going to solve a service time problem.
And B) the "simultaneous read" benefit is outweighed by the inevitable increase in sharing that must result from this scheme. Consider, if Raid 50 stripes multiple Raid 5's together, then the resulting volume must be multiple times the size. This means that the SAN manager has much larger, but fewer Volumes to carve up: That's good for them, but bad for us, because it makes it that much more likely that some other usage of the same Raid 50 volume will be competing for the drive heads at the same time and that is very bad for SQL Server performance.
My advice: this is yet another example of the SAN Vendors failing to understand the real needs of DBA's and DBMS's: stick with Raid 10.
[font="Times New Roman"]-- RBarryYoung[/font], [font="Times New Roman"] (302)375-0451[/font] blog: MovingSQL.com, Twitter: @RBarryYoung[font="Arial Black"]
Proactive Performance Solutions, Inc. [/font][font="Verdana"] "Performance is our middle name."[/font]
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