April 6, 2010 at 3:23 pm
Hi,
We are using perfmon to monitor the sql instance. The storage for this sql instance is from SAN.
we have the disks as below:
C- OS
D- data files
E- log files
T- TempDB
Z- backups
Each disk has 150 spindles in it.
Perfmon giving High Avg.Disk Queue length alarms of values up to 33 some times.
So is Perfmon takes consideration of the no.of spindles in each disk & then measures the Avg.Queue length? or
do we need to divide Avg.Disk Queue length that Perfmon giving by the no.of spindles in each disk? for example 33/150 = 0.22 , which <2 & has no disk contention right?
Please clarify me
April 6, 2010 at 4:19 pm
rambilla4 (4/6/2010)
Hi,Perfmon giving High Avg.Disk Queue length alarms of values up to 33 some times.
So is Perfmon takes consideration of the no.of spindles in each disk & then measures the Avg.Queue length? or
Please clarify me
Perfmon has no idea, the OS simply see's each disk as an individual volume, it does not know what that volume consists of. Each disk is simply a disk to the operating system.
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April 6, 2010 at 5:09 pm
Perfmon has no idea, the OS simply see's each disk as an individual volume, it does not know what that volume consists of. Each disk is simply a disk to the operating system
So is the below formula correct?
actual Avg.Disk Queue length = Avg.Disk Queue length value from perfmon/no.of spindles in disk
thanks
April 7, 2010 at 12:47 pm
The question about perform's avg disk queue length and its usefulness has come up before on this forum. Here is one of the other conversations about it with a couple of good tips:
http://www.sqlservercentral.com/Forums/Topic823698-146-1.aspx
There are probably others as well. If I were you I'd start by searching for other ways to measure disk subsystem performance in regards to SQL Server besides avg disk queue length.
Steve
SQL Managed
April 8, 2010 at 8:30 am
ADQL is completely useless as a disk performance metric in the modern age. Use avg disk sec/read and avg disk sec/write instead. Even better, use the SQL Server DMV sys.dm_io_virtual_file_stats to determine the IO stalls from SQL Server's perspective - that is what truly matters anyway.
Best,
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru on googles mail service
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