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Poor SAN Performance

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Steve Saindon
Poor SAN Performance
on Feb 1, 2011 at 3:19:45 pm

I am having very high read wait times on our OLTP system and would like to prove to our SAN vendor that we need to make changes. I recently modified our disk configuration but the changes didn’t make any difference. Our current configuration is as follows:

Primary data file - dedicated 8 disk raid 10 lun
Index file (which contains all of the non-clustered indexes) - dedicated 6 disk raid 10 lun
Log file – dedicated 4 disk raid 10 lun
TempDB – dedicated 4 disk raid 10 lun.

Here are my performance numbers:

Primary Data File (50 GB)
Avg Read Wait -113 ms
Avg Write Wait - 16 ms

Index File (50 GB)
Avg Read Wait - 119 ms
Avg Write Wait - 53 ms

Log File
Avg Read Wait - 9 ms
Avg Write Wait - 3 ms

TempDB - split into 4 files but here is the average
Avg Read Wait - 4 ms
Avg Write Wait - 30 ms.

Our system does about 10 million reads and 2.5 million writes a day.

My main concern are the read wait times on the Primary and Index files. I also am concerned with the Write wait times on the Index and TempDB files. My understanding is that all wait times should be less than 20 ms.

As mentioned, I would like some comparison numbers to show my SAN vendor. Would anyone please run the following code and post the results? This script is for SQL Server.

Let me know if anyone has suggestions on how to get better performance outside of the SAN configuration. Are there any different SQL setting, configurations that I could implement to improve read write performance?

Thanks for the help.

select db_name(mf.database_id) as databaseName, mf.physical_name,
num_of_reads, io_stall_read_ms, AvgReadWait=io_stall_read_ms/num_of_reads,
num_of_writes, io_stall_write_ms, AvgWriteWait=io_stall_write_ms/num_of_writes,
from sys.dm_io_virtual_file_stats(null,null) as divfs
join sys.master_files as mf
on mf.database_id = divfs.database_id
and mf.file_id = divfs.file_id
WHERE db_name(mf.database_id) in ('EnterDatabaseName','tempdb')

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