July 2, 2010 at 4:02 pm
Hello - we are in the process of acquiring a new production database server running SQL 2008, which will be SAN attached. Our previous setup was a Direct attached drive array. I know that keeping the data, log, and tempdb files all on separate physical disk drives is a good practice to maximize concurrent I/O. I am a DBA, and the group that handles the SAN is a separate entity. My question is this:
Since the SAN is already made up of multiple drives across potentially multiple drive arrays, when the SAN storage is allocated for this server, is there really any real I/O performance advantage to me creating separate partitions of the assigned LUN from the SAN for my log files, data files, and tempdb? I am not able to distinguish different physical drives anyway, and the underlying storage space is already multiple RAID sets. Thanks.
Joe
July 2, 2010 at 9:14 pm
Well - the standard answer applies here: it depends...:-)
It depends a lot on the SAN that you are using, how that SAN has been configured and how the LUN's are being carved out of the SAN.
For example, on an HP EVA 8000 - you can have a very large disk group with say 120 physical drives. You would carve multiple LUN's from that disk group and present to a number of servers. You could run into problems with this if you have a lot of very active systems all accessing the same disk group. If you only put one or two active systems - and the other systems are not that active, you wouldn't even notice any difference.
Other SAN's are configured differently and it could matter how you carve it out.
With that said, I still carve out separate LUN's for system databases, data files, log files, backup and tempDB. Even though it doesn't really matter for IO - I prefer this method so I can logically manage the storage better.
I would recommend that you sit with your storage team to understand how the SAN is setup and configured and determine the best model for that setup.
Jeffrey Williams
“We are all faced with a series of great opportunities brilliantly disguised as impossible situations.”
― Charles R. Swindoll
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