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

Administering a System: Managing Disks and Files
Managing Swap and Dump
Chapter 6 663
requires the system to perform a greater amount of processing and is
usually slower than device swap, it should not be used as a permanent
replacement for a sufficient amount of device swap space.
The file system used for swap can be either a local or a remote file
system. Cluster clients can use remote file system swap for their swap
needs. Swapping to a remote file system is slower than swapping to a
local file system and is not encouraged if local device swap or local file
system swap is available.
Pseudo-Swap
Pseudo-swap space allows for the use of system memory as a third
type of swap space. That is, HP-UX swap space can also consist of up to
seven-eighths (87.5%) of system memory capacity.
For example, a computer with one GB of system memory and one GB of
device and file system swap, can run up to 1.87GB of processes. If any
process attempts to grow or be created beyond this extended threshold,
the process will fail.
When using pseudo-swap, since more processes can be created, the
system load increases, causing more paging and deactivation activity.
By default, pseudo-swap space is configured to be available. If you do not
wish to make use of it, you will need to reset the tunable system
parameter, swapmem_on, to 0 (“off”).
Primary and Secondary Swap
Your system must have at least one device swap area available when it
boots. This area is known as the primary swap area. (Primary swap is
not mandatory if pseudo-swap is enabled, however, it is strongly
recommended.) Primary swap, by default, is located on the same disk as
the root file system. By default, the system’s kernel configuration file
/stand/system contains the configuration information for primary
swap.
Other swap may be used in addition to primary swap. Such swap is
referred to as secondary swap. If you are using device swap as
secondary swap, allocate such secondary swap to reside on a disk other
than the root disk for better performance. File system swap is always
secondary swap.