HP SureStore E SAN Manager LUN Management Administrator's Guide

Diskperf and Performance Monitor 167
Advanced SAN
Administration
Diskperf and Performance Monitor
Diskperf (a filter driver) layers over disk drivers such as SAN Manager LM’s Disk Driver
(trdisk). All disk I/O originating in higher-level drivers and applications passes through
Diskperf, which collects performance statistics and reports them to the Performance
Monitor application.
Potential Problems
• The filter driver is not loaded until it is enabled (diskperf -y) and the computer is
restarted.
• The filter has to attach to the disk before the file system mounts the disk. If the file
system mounts first, the filter cannot insert itself between the file system and disk, so
none of the file system activity is noted. For this reason, starting the Diskperf driver in
the Devices control panel will not allow you to collect performance information
because the file system drivers have already mounted the disk.
• The filter driver only looks for and attaches to disks when it is loaded—at startup. If
devices are assigned to the machine afterwards, the filter driver will not filter them
and no performance information can be collected for them.
• SAN Manager LM allows you to unassign devices from a host with Diskperf loaded, but
if you assign the device to the host again, Diskperf will not filter it until the host is
rebooted.