Dynamic Multi-Pathing 7.3.1 Administrator's Guide - Linux

Configuring the I/O throttling mechanism

By default, Dynamic Multi-Pathing (DMP) is configured with I/O throttling turned off for all paths. To display the current settings for I/O throttling that are applied to the paths to an enclosure, array name, or array type, use the vxdmpadm getattr command.

If enabled, I/O throttling imposes a small overhead on CPU and memory usage because of the activity of the statistics-gathering daemon. If I/O throttling is disabled, the daemon no longer collects statistics, and remains inactive until I/O throttling is re-enabled.

To turn off I/O throttling, use the following form of the vxdmpadm setattr command:

# vxdmpadm setattr \
  {enclosure enc-name|arrayname name|arraytype type} \
  recoveryoption=nothrottle

The following example shows how to disable I/O throttling for the paths to the enclosure enc0:

# vxdmpadm setattr enclosure enc0 recoveryoption=nothrottle

The vxdmpadm setattr command can be used to enable I/O throttling on the paths to a specified enclosure, disk array name, or type of array:

# vxdmpadm setattr \
  {enclosure enc-name|arrayname name|arraytype type}\
  recoveryoption=throttle [iotimeout=seconds]

If the iotimeout attribute is specified, its argument specifies the time in seconds that DMP waits for an outstanding I/O request to succeed before invoking I/O throttling on the path. The default value of iotimeout is 10 seconds. Setting iotimeout to a larger value potentially causes more I/O requests to become queued up in the SCSI driver before I/O throttling is invoked.

The following example sets the value of iotimeout to 60 seconds for the enclosure enc0:

# vxdmpadm setattr enclosure enc0 recoveryoption=throttle \
  iotimeout=60

Specify recoveryoption=default to reset I/O throttling to the default settings, as follows:

# vxdmpadm setattr arraytype A/A recoveryoption=default

The above command configures the default behavior, corresponding to recoveryoption=nothrottle. The above command also configures the default behavior for the response to I/O failures.