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

Administering a System: Managing Disks and Files
Managing Swap and Dump
Chapter 6668
• Interleave file system swap areas for best performance.
The use of interleaving on separate disks is described under
“Guidelines for Setting Up Device Swap Areas” on page 667.
• To keep good system performance, avoid using heavily used file
systems such as the root (/) for file system swap.
Use the bdf command to check file systems for available space.
• Use SAM or the swapinfo command to show information about file
systems for which swap might be already enabled.
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). The system uses the swap
areas with higher priority first. The system 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.
• Give device swap areas priority over file system swap areas.
• Give lower use file systems priority over higher use file systems.
The primary swap area has priority 1. Device and file system swap areas
set dynamically default to a priority of 1 if no priority is specified.
Adding, Modifying, or Removing File System Swap
At times when the designated device swap is insufficient, you can
configure to allow a process to use an existing file system for swapping.
When you enable a file system for swap, the operating system can swap
to unused portions of the file system as needed. Unless you pre-allocate
the swap space using the min option of the swapon command, file system
swap which has not been recently used will be freed back to the file
system when it needs the space.