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475Performance monitoring and tuning
Tuning VxVM
Tunable parameters
The following sections describe specific tunable parameters.
dmp_cache_open
If set to on, the first open of a device that is performed by an array support
library (ASL) is cached. This enhances the performance of device discovery by
minimizing the overhead caused by subsequent opens by ASLs. If set to
off,
caching is not performed. The default value is
off.
The value of this tunable is changed by using the
vxdmpadm settune command.
dmp_daemon_count
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.
The value of this tunable is changed by using the
vxdmpadm settune command.
dmp_delayq_interval
How long DMP should wait before retrying I/O after an array fails over to a
standby path. Some disk arrays are not be capable of accepting I/O requests
immediately after failover.
The default value is 15 seconds.
The value of this tunable is changed by using the vxdmpadm settune command.
“Configuring DMP path restoration policies” on
page 160dmp_failed_io_threshold
The time limit that DMP waits for a failed I/O request to return before the device
is marked as INSANE, I/O is avoided on the path, and any remaining failed I/O
requests are returned to the application layer without performing any error
analysis.
The default value is 57600 seconds (16 hours).
The value of this tunable is changed by using the
vxdmpadm settune command.
dmp_fast_recovery
Whether DMP should attempt to obtain SCSI error information directly from the
HBA interface. Setting the value to on can potentially provide faster error
recovery, provided that the HBA interface supports the error enquiry feature.
If set to
off, the HBA interface is not used. This is the default setting.