VERITAS Volume Manager 4.1 Administrator's Guide

Administering Dynamic Multipathing (DMP)
Administering DMP Using vxdmpadm
Chapter 3142
The default value for the partition size is 1024 blocks (1MB). A value that is not a power of 2
is silently rounded down to the nearest acceptable value. Specifying a partition size of 0 is
equivalent to the default partition size of 1024 blocks (1MB). For example, the suggested
partition size for an Hitachi HDS 9960 A/A array is from 16,384 to 65,536 blocks (16MB to
64MB) for an I/O activity pattern that consists mostly of sequential reads or writes.
NOTE The benefit of this policy is lost if the value is set larger than the cache size.
The default value can be changed by adjusting the value of a tunable parameter (see
“dmp_pathswitch_blks_shift” on page 417) and rebooting the system.
The next example sets the balanced I/O policy with a partition size of 2048 blocks (2MB) on
the enclosure enc0:
# vxdmpadm setattr enclosure enc0 iopolicy=balanced \
partitionsize=2048
• minimumq
This policy sends I/O on paths that have the minimum number of outstanding I/O
requests in the queue for a LUN. This is suitable for low-end disks or JBODs where a
significant track cache does not exist. No further configuration is possible as DMP
automatically determines the path with the shortest queue.
The following example sets the I/O policy to minimumq for a JBOD:
# vxdmpadm setattr enclosure Disk iopolicy=minimumq
64 65,536
128 131,072
256 262,144
512 524,288
1024(default) 1,048,576
2048 2,097,152
4096 4,194,304
Table 3-1 Partition Size in Blocks and Bytes (Continued)
Partition Size in
Blocks
Equivalent Size in
Bytes