HP Veritas Volume Manager 5.0 -UX 11i v3 manual Following policies may be set, Adaptiveminq

148Administering dynamic multipathing (DMP)

Administering DMP using vxdmpadm

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

■adaptiveminq

Similar to the adaptive policy, except that I/O is scheduled according to the length of the I/O queue on each path. The path with the shortest queue is assigned the highest priority.

■balanced [partitionsize=size]

This policy is designed to optimize the use of caching in disk drives and RAID controllers. 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.