HP-UX System Administrator's Guide: Overview HP-UX 11i v3 (B3921-90011, September 2010)

If you have only one disk and need to increase swap space, try to move the primary swap
area to a larger region on the disk.
To see which devices are already being used for device swap use the command:
swapinfo -d
Try to keep multiple device swap areas similar in size.
Device swap areas should have similar sizes for best performance. When you configure
swap areas of different sizes, when all space in the smaller device swap area is used only
the larger swap area is available making interleaving no longer possible and slowing down
paging performance.
The nswapdev tunable system parameter controls the maximum number of swap devices.
Although the default value for nswapdev is large enough to accommodate nearly all HP-UX
systems, verify that it is large enough to accommodate the number of swap areas you require.
File System Swap Guidelines
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:
Interleave file system swap areas for best performance.
Two swap areas on different disks perform better than one swap area with the equivalent
amount of space. Multiple devices allow for interleaved swapping which means the swap
areas are written to concurrently, minimizing disk head movement, thus enhancing
performance. This applies as much to file system swap space as it does to device swap space,
so the same guideline applies.
To see which devices are already being used for file system swap use the command:
swapinfo -f
If possible, avoid configuring heavily used file systems. Heavily used has two meanings
here:
1. Actively used file systems (for example, the root file system, or those file systems used
most frequently by your primary applications). This will slow down the performance
of your server as paging activities compete with your applications and user file access.
2. Very full file systems. Because file system swap uses unused space within file systems, if
the file systems are very full there is not much unused space for paging use (and it is
probably very fragmented within the file system). To gauge how full a file systems are,
use the bdf command.
Guidelines for Assigning Swap Priority
When you add swap areas, you can assign a priority to each. Priorities range from 0 (the highest)
to 10 (the lowest). HP-UX uses swap areas with higher priority first. And, HP-UX gives device
swap priority over file system swap when each has the same priority. Here are the guidelines
you should use:
Given multiple swap devices with identical performance, assign each an identical priority.
By so doing, you will allow the system to use each of them on an interleaved basis which
enhances performance.
Assign higher priorities to the swap areas that have faster performance and lower priorities
to areas that are slower.
Do not give file system swap areas priority over device system swap areas. Although this
is not absolutely necessary it enhances the swapinfo output.
Give lower use file systems priority over higher use file systems.
Storage on HP-UX 63