04 July 2012

Average I/O stalls

by Stuart Ainsworth

55,785 0 I/O, Performance

This is a general indicator of performance problems. High stall times indicate I/O problems, which can be attributed to busy physical disks or queries that return large data sets to the client.

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Guideline values: The ideal value for this metric should be less than 100, but this is just a rule-of-thumb. Higher values may be acceptable for your organization.

Check also:

Disk avg. read time
Disk avg. write time
Avg. disk queue length

Possible solutions:
IO Stalls are affected by three possible factors:

poorly performing disk subsystem (such as a misconfigured SAN)
poorly defined queries
overloaded disks (“data bursts”)

Solutions may involve allocating new hardware resources in addition to performance tuning of individual queries.

More information:

Wikis: Disk Contention Issues

Troubleshooting SQL Server I/O requests taking longer than 15 seconds – I/O stalls & Disk latency

Metric definition

Name

Average IO stalls

Description

Explanation: This is a general indicator of performance problems. High stall times indicate I/O problems, which can be attributed to busy physical disks or queries that return large data sets to the client. Guideline values: The ideal value for this metric should be less than 100, but this is just a rule-of-thumb. Higher values may be acceptable for your organization. Check also:

Disk avg. read time
Disk avg. write time
Avg. disk queue length

Possible solutions: IO Stalls are affected by three possible factors:

poorly performing disk subsystem (such as a misconfigured SAN)
poorly defined queries
overloaded disks (“data bursts”)

Solutions may involve allocating new hardware resources in addition to performance tuning of individual queries.

More information:

Wikis: Disk Contention Issues

Troubleshooting SQL Server I/O requests taking longer than 15 seconds - I/O stalls & Disk latency

The T-SQL query that will collect data


		
			
			
Transact-SQL
			
			SELECT  CAST(SUM(io_stall_read_ms + io_stall_write_ms) /
             SUM(1.0 + num_of_reads + num_of_writes) AS NUMERIC(10, 1)
        ) AS [avg_io_stall_ms]
FROM    sys.dm_io_virtual_file_stats(DB_ID(), NULL)
WHERE   FILE_ID <> 2;
			
				
					
				
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						SELECT  CAST(SUM(io_stall_read_ms + io_stall_write_ms) /
             SUM(1.0 + num_of_reads + num_of_writes) AS NUMERIC(10, 1)
        ) AS [avg_io_stall_ms]
FROM    sys.dm_io_virtual_file_stats(DB_ID(), NULL)
WHERE   FILE_ID <> 2;

Instances to collect from

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Databases to collect from

Collection frequency

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Metric collection

Enabled

Alert definition

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Average I/O stalls

Metric definition

Name

Description

The T-SQL query that will collect data

Instances to collect from

Databases to collect from

Collection frequency

Use collected or calculated values

Metric collection

Alert definition

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