Performance | IO

A graphical report showing average I/O metrics. This is a mixture of current data, and averages from cumulative data captured since the last service restart.

Average I/O/sec

This chart displays the total number of reads and writes for data and log files, and divides the figures by number of seconds since the service started, to give average number of I/Os per second.

Average Throughput MB/sec

This chart displays the total read and write throughput for data and log files, and divides the figures by number of seconds since the service started, to give average throughput in MB per second.

Average Stall (ms)

This chart displays the nearest you can get to measuring disk read and write latency from SQL Server without viewing the server-level performance counters (which are not available through sys.dm_os_performance_counters). The data is calculated by taking the total read and write stalls from the virtual file stats and dividing by the number of stalls.

Average I/O waits (ms)

This chart displays the I/O waits from sys.dm_os_wait_stats, and calculates the average for each. These figures are accurate from the last time the wait stats were cleared, which is either the last service restart or the last time they were manually cleared using DBCC SQLPERF.

Log flushes

This table shows log flush performance

What It ShowsComments
Log MB flushed/secAverage throughput of log flushes per second
Log flushes/secAverage number of times the log is flushed per second
Log flush wait time (ms)This is not an average - it examines the current log flush wait time for all the databases and displays the highest. The figure is highlighted if it goes above 32ms.

Tasks waiting on I/O

The number of tasks waiting on I/O should be close to zero if I/O is not a bottle-neck.

What It ShowsComments
Waiting tasks
Total duration (ms)The total wait time for all tasks waiting on I/O

Pending I/O requests

What It ShowsComments

The number of pending I/O requests, taken from sys.dm_io_pending_io_requests.

Pending I/Os
Total duration (ms)
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