Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

DMP tunable parameters
Table 15-2 shows the DMP parameters that can be tuned by using the vxdmpadm
settune command.
Table 15-2
DMP parameters that are tunable
DescriptionParameter
If this parameter is set to on, the first open of a device
that is performed by an array support library (ASL)
is cached. This caching enhances the performance of
device discovery by minimizing the overhead that is
caused by subsequent opens by ASLs. If this parameter
is set to off, caching is not performed.
The default value is on.
dmp_cache_open
The number of kernel threads that are available for
servicing path error handling, path restoration, and
other DMP administrative tasks.
The default number of threads is 10.
dmp_daemon_count
How long DMP should wait before retrying I/O after
an array fails over to a standby path. Some disk arrays
are not capable of accepting I/O requests immediately
after failover.
The default value is 15 seconds.
dmp_delayq_interval
If this parameter is set to on, it enables the path
restoration thread to be started.
See “Configuring DMP path restoration policies”
on page 194.
If this parameter is set to off, it disables the path
restoration thread. If the path restoration thread is
currently running, use the vxdmpadm stop restore
command to stop the thread.
The default is on.
See “Stopping the DMP path restoration thread”
on page 195.
dmp_enable_restore
Performance monitoring and tuning
Tuning VxVM
504