Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Administering DMP Using vxdmpadm
122 VERITAS Volume Manager Administrator’s Guide
In this example, the adaptive I/O policy is set for the enclosure enc1:
# vxdmpadm setattr enclosure enc1 iopolicy=adaptive
◆ balanced [partitionsize=size]
This policy is designed to optimize the use of caching in disk drives and RAID
controllers, and is the default policy for A/A arrays. The size of the cache typically
ranges from 120KB to 500KB or more, depending on the characteristics of the
particular hardware. During normal operation, the disks (or LUNs) are logically
divided into a number of regions (or partitions), and I/O from/to a given region is
sent on only one of the active paths. Should that path fail, the workload is
automatically redistributed across the remaining paths.
You can use the size argument to the partitionsize attribute to specify the
partition size. The partition size in blocks is adjustable in powers of 2 from 2 up to
2^31 as illustrated in the table below:
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.
Partition Size in Blocks Equivalent Size in Bytes
22,048
44,096
88,192
16 16,384
32 32,768
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