Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

149Administering dynamic multipathing (DMP)
Administering DMP using vxdmpadm
The value of the argument to retrycount specifies the number of retries to be attempted
before DMP reschedules the I/O request on another available path, or fails the request
altogether.
As an alternative to specifying a fixed number of retries, the following version of the
command specifies how long DMP should allow an I/O request to be retried on a path:
# vxdmpadm setattr \
{enclosure enc-name|arrayname name|arraytype type} \
recoveryoption=timebound iotimeout==seconds
The value of the argument to iotimeout specifies the time in seconds that DMP waits for
an outstanding I/O request to succeed before it reschedules the request on another
available path, or fails the I/O request altogether. The effective number of retries is the
value of
iotimeout divided by the sum of the times taken for each retry attempt. DMP
abandons retrying to send the I/O request before the specified time limit has expired if it
predicts that the next retry will take the total elapsed time over this limit.
The default value of iotimeout is 10 seconds. For some applications, such as Oracle, it
may be desirable to set
iotimeout to a larger value, such as 60 seconds.
Note: The fixedretry and timebound settings are mutually exclusive.
The following example configures time-bound recovery for the enclosure enc0, and sets
the value of iotimeout to 60 seconds:
# vxdmpadm setattr enclosure enc0 recoveryoption=timebound \
iotimeout=60
The next example sets a fixed-retry limit of 10 for the paths to all Active/Active arrays:
# vxdmpadm setattr arraytype A/A recoveryoption=fixedretry \
retrycount=10
Specifying recoveryoption=default resets DMP to the default settings corresponding
to
recoveryoption=fixedretry retrycount=5, for example:
# vxdmpadm setattr arraytype A/A recoveryoption=default
This command also has the effect of configuring I/O throttling with a queue depth of 20 on
the paths. See “Configuring the I/O throttling mechanism” on page 149 for details.
Note: The response to I/O failure settings is persistent across reboots of the system.
Configuring the I/O throttling mechanism
By default, I/O throttling is turned on for all paths with a maximum of 20 outstanding I/O
requests on each path. 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: