Working with DASD statistics in debugfs

The DASD performance data is contained in the following subdirectories of <mountpoint>/dasd, where <mountpoint> is the mount point of debugfs:

• A directory global that represents all available DASDs taken together.
• For each DASD, one directory with the name of the DASD block device with which the DASD is known to the DASD device driver (for example, dasda, dasdb, and dasdc).
• For each CCW device that corresponds to a DASD, a directory with the bus ID as the name.

  Block devices that are not set up for PAV or HyperPAV map to exactly one CCW device and the corresponding directories contain the same statistics.

  With PAV or HyperPAV, a bus ID can represent a base device or an alias device. Each base device is associated with a particular block device. The alias devices are not permanently associated with the same block device. At any one time, a DASD block device is associated with one or more CCW devices. Statistics that are based on bus ID, therefore, show more detail for PAV and HyperPAV setups.

Each of these directories contains a file statistics that you can use to perform these tasks:

• Start and stop data gathering.
• Reset statistics counters.
• Read statistics.

To control data gathering at the scope of a directory in <mountpoint>/dasd, issue a command of this form:

# echo <keyword> > <mountpoint>/dasd/<directory>/statistics

Where:

<directory>

is one of the directories in <mountpoint>/dasd.

<keyword>

specifies the action to be taken:

on

to start data gathering.

off

to stop data gathering.

reset

to reset the statistics counters.

To read performance data, issue a command of this form:

# cat <mountpoint>/dasd/<directory>/statistics