VERITAS Volume Manager 4.1 Administrator's Guide

Administering Dynamic Multipathing (DMP)
Administering DMP Using vxdmpadm
Chapter 3 141
NOTE Starting with release 4.1 of VxVM, I/O policies are recorded in the file
/etc/vx/dmppolicy.info, and are persistent across reboots of the system. Do
not edit this file yourself.
The following policies may be set:
• adaptive
This policy attempts to maximize overall I/O throughput from/to the disks by dynamically
scheduling I/O on the paths. It is suggested for use where I/O loads can vary over time.
For example, I/O from/to a database may exhibit both long transfers (table scans) and
short transfers (random look ups). The policy is also useful for a SAN environment where
different paths may have different number of hops. No further configuration is possible as
this policy is automatically managed by DMP.
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.
Table 3-1 Partition Size in Blocks and Bytes
Partition Size in
Blocks
Equivalent Size in
Bytes
2 2,048
4 4,096
8 8,192
16 16,384
32 32,786