Managing Systems and Workgroups: A Guide for HP-UX System Administrators

Administering a System: Managing Disks and Files
Managing Swap and Dump
Chapter 6 667
For example, when the value of the parameter maxswapchunks is 256,
the maximum configurable device swap space (maxswapchunks x
swchunk x DEV_BSIZE ) is:
256 x 2 MB = 512 MB
If you need to increase the limit of configurable swap space beyond the
default, increase the value of the maxswapchunks operating system
parameter either by using SAM (which has more information on tunable
parameters) or reconfigure the kernel using HP-UX commands. The
parameter swchunk is also tunable.
Guidelines for Setting Up Device Swap Areas
• Interleave device swap areas for better performance.
Two swap areas on different disks perform better than one swap area
with the equivalent amount of space. This allows interleaved
swapping which means the swap areas are written to concurrently,
minimizing disk head movement, thus enhancing performance. (See
“Guidelines for Assigning Swap Priority” on page 668.)
When using LVM, you should set up secondary swap areas within
logical volumes that are on different disks (physical volumes) using
lvextend.
If you have only one disk and need to increase swap space, then you
should try to move the primary swap area to a larger region.
• Similar-sized device swap areas work best.
Device swap areas should have similar sizes for best performance.
Otherwise, when all space in the smaller device swap area is used,
only the larger swap area is available, making interleaving no longer
possible.
• The nswapdev tunable system parameter controls the maximum
number of swap devices. SAM has more information on tunable
parameters.
Guidelines for Setting Up File System Swap Areas
When you need more swap space and you have no devices available for
additional device swap, or if you need to swap to a remote system, you
can dynamically add file system swap to your system. Use the following
guidelines: