Compressed Dump

Compressed Dump White Paper, Version 1.3
page 1
1. Objective
The objective of this document is to describe the Compressed Dump functionality that will be introduced in
HP-UX 11i, v2 in the kernel dump subsystem. The features implemented by the Compressed Dump project
will be a standard feature for future releases of HP-UX starting from 11i v2.
2. Introduction
The goal of the Compressed Dump feature is to speedup the memory dump for HP-UX in the event of a
system crash, so that dumps are taken faster and system availability is improved. This feature is primarily
targeted for “large memory machines” running 11i v2 or any later release.
3. Compressed Dump Features
The Compressed Dump functionality affects dump configuration, dump-time console user-interface, dump
file format, access library, and dump manipulation commands.
• This feature will be available to all platforms having more than 4 processors and physical memory
more than 2GB, supported in 11i v2.
• With the Compressed Dump feature, kernel dump+save times are speeded up. The actual
speedup and dump space usage depends on various factors like the throughput of the device con-
figured for dump and the compressibility of memory.
With devices that give less than 15MB/sec of sustained throughput for uncompressed dumps,
enabling compression will give a speedup of at least 3x for dumping the default selection of page
classes. The disk space requirement should also be reduced by at least a factor of 3X for the
default selection of page classes. The down-time of the system is consequently reduced.
NOTE: On a machine that took X hrs. of time to dump, with the option of Compressed Dump,
the dump time should reduce to X/3 hrs. at least (this includes the time for savecrash
to copy the dump image to disk).
Typical speed-up seen when dumping compressed, the default class of pages
selected, KSDATA, KDDATA, FSDATA and USTACK, is around 7.
If the system is crashed soon after a boot where most of the memory pages are not
touched by the OS, and if UNUSED class is also included in the dump, then Com-
pressed Dump performance may be as slow as uncompressed dump. This is because
the UNUSED pages contain mostly incompressible random data.
If the crash occurs after the system has been under heavy use, then Compressed
Dump including UNUSED pages may also show good performance.