HP-UX Workload Manager User's Guide

Understanding how PRM manages resources
Management of disk bandwidth
Appendix F452
Management of disk bandwidth
PRM manages disk bandwidth at the logical volume group level. As such,
your disks must be mounted and under the control of Logical Volume
Manager (LVM) to take advantage of PRM disk bandwidth management.
LVM divides the disk in much the same way as the hard partitions
implemented under previous versions of HP-UX for the Series 800
systems. However, logical volumes are much easier to reconfigure than
partitions, and they can span two or more disks. These two attributes
make LVM a much more powerful and flexible tool than hard partitions.
LVM uses the concept of a volume group, which is a collection of one or
more disks. A volume group can be divided into several partitions, which
are called logical volumes.
NOTE When setting up LVM, do not create swap partitions in any volume group
that is under PRM control.
For information on using LVM, see Managing Systems and Workgroups:
A Guide for HP-UX System Administrators. This book is available on the
Web at http://docs.hp.com.
PRM controls disk bandwidth by re-ordering a volume group’s I/O
requests. This has the effect of delaying the I/O requests of low-priority
processes and accelerating those of higher-priority processes.
Disk bandwidth management works only when there is contention for
disk bandwidth, and it works only for actual I/O to the disk. (Commonly,
I/O on HP-UX is staged through the buffer cache to minimize or
eliminate as much disk I/O as possible.)
Disk bandwidth management works on disk devices, stripes, and disk
arrays. It does not work on tape or network devices.
When you change share allocations on a busy disk device, it typically
takes 30 seconds for the actual bandwidth to conform to the new
allocations.