JetStress: Database Fault Stalls/sec should be zero on production servers.

Exchange servers should generally have database write latencies under 20 ms, with spikes (maximum values) under 50 ms. However, it is not always possible to keep write latencies in this range when synchronous replication is in use. Database write latency issues often do not become apparent to the end user until the database cache is full and cannot be written to. When using synchronous replication, the Performance Monitor Database Page Fault Stalls/sec counter is a better indicator of whether the client is being affected by write latency than the PhysicalDisk\Average Disk sec/Write counter.

On a production server, the value of the Database Page Fault Stalls/sec counter should always be zero, because a database page fault stall indicates that the database cache is full. A full database cache means that Exchange is unable to place items in cache until pages are committed to disk. Moreover, on most storage subsystems, read latencies are affected by write latencies. These read latencies may not be detectable at the default storage subsystem Performance Monitor sampling rate. Remote procedure call (RPC) latencies also increase as a consequence of database page fault stalls, which can degrade the client experience.

Because disk-related performance problems can negatively affect the user experience, it is recommended that administrators monitor disk performance as part of routine system health monitoring. When analyzing a database logical unit number (LUN) in a synchronously replicated environment, you can use the counters listed in the following table to determine whether there is any performance degradation on the disks.

Performance Monitor Counters for Database Disk Performance Evaluation

Performance Monitor Counter

Expected values

PhysicalDisk\Average Disk sec/Read

Indicates the average time (in seconds) to read data from the disk.

The average value should be below 20 ms.

Spikes (maximum values) should not be higher than 50 ms.

PhysicalDisk\Average Disk sec/Write

Indicates the average time (in seconds) to write data to the disk.

This counter is not a good indicator for client latency in a synchronous replication environment

Database\Database Page Fault Stalls/sec

Indicates the rate of page faults that cannot be serviced because there are no pages available for allocation from the database cache.

This counter should be zero on production servers.

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