Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

Table 16-2
DMP parameters that are tunable (continued)
DescriptionParameter
Whether the Event Source daemon (vxesd) uses the Storage
Networking Industry Association (SNIA) HBA API. This API
allows DDL to improve the performance of failover by
collecting information about the SAN topology and by
monitoring fabric events.
If this parameter is set to on, DDL uses the SNIA HBA API.
(Note that the HBA vendor specific HBA-API library should
be available to use this feature.)
If this parameter is set to off, the SNIA HBA API is not
used.
The default setting is off for releases before 5.0 that have
been patched to support this DDL feature. The default
setting is on for 5.0 and later releases.
dmp_monitor_fabric
The time for which an intermittently failing path needs to
be monitored as healthy before DMP again tries to schedule
I/O requests on it.
The default value is 300 seconds.
A value of 0 prevents DMP from detecting intermittently
failing paths.
dmp_path_age
The default number of contiguous I/O blocks that are sent
along a DMP path to an array before switching to the next
available path. The value is expressed as the integer
exponent of a power of 2; for example 9 represents 512
blocks.
The default value of this parameter is set to 9. In this case,
1024 blocks (1MB) of contiguous I/O are sent over a DMP
path before switching. For intelligent disk arrays with
internal data caches, better throughput may be obtained by
increasing the value of this tunable. For example, for the
HDS 9960 A/A array, the optimal value is between 14 and
16 for an I/O activity pattern that consists mostly of
sequential reads or writes.
This parameter only affects the behavior of the balanced
I/O policy. A value of 0 disables multipathing for the policy
unless the vxdmpadm command is used to specify a different
partition size for an array.
See “Specifying the I/O policy” on page 175.
dmp_pathswitch_blks_shift
543Performance monitoring and tuning
Tuning VxVM