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156 Administering dynamic multipathing (DMP)
Administering DMP using vxdmpadm
Configuring the response to I/O failures
By default, DMP is configured to retry a failed I/O request up to 5 times for a
single path. To display the current settings for handling I/O request failures that
are applied to the paths to an enclosure, array name or array type, use the
vxdmpadm getattr command:
# vxdmpadm getattr \
{enclosure enc-name|arrayname name|arraytype type} \
recoveryoption
See “Displaying recoveryoption values” on page 159 for more information.
The following example displays the I/O request failure setting for the paths to
the enclosure enc0:
# vxdmpadm getattr enclosure enc0 recoveryoption
The vxdmpadm setattr command can be used to configure how DMP responds
to failed I/O requests on the paths to a specified enclosure, disk array name, or
type of array.
The following form of the command sets a limit for the number of times that
DMP will attempt to retry sending an I/O request on a path:
# vxdmpadm setattr \
{enclosure enc-name|arrayname name|arraytype type} \
recoveryoption=fixedretry retrycount==n
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.