HP-UX Compressed Dump Release Notes
HP-UX Compressed Dump Release Notes
What’s in This Version
Chapter 18
The compression option is turned ON by default.
The init script option for crashconf sets the compression option every time the system boots
up. Setting CRASHCONF_COMPRESS to 1 in /etc/rc.config.d/crashconf turns compressed
dump ON whenever the system boots up. Setting it to 0 turns compressed dump OFF. Not
setting it, will not change the default compression hint in the kernel, which is to dump
compressed.
pstat_getcrashinfo [pstat (2)] can be used to query the current crashdump configuration.
The field psc_flags field in the structure pst_crashinfo indicates the state of compressed
dump. The flag values for psc_flags are:
#define PS_EARLY_DUMP 0x1 /* An early dump was taken */
#define PS_CONF_CHANGED 0x2 /* Config. changed since boot */
#define PS_HEADER_VALID 0x4 /* headerdev and headeroffset valid */
#define PS_COMPRESS 0x8 /* Compress dump state */
The compression option is just a hint to the kernel to use the Compressed Dump feature.
During a system crash, the dump sub-system examines the state of the system and its
resources to determine whether it is possible to use compression. Depending on the resources
available, the system decides dynamically whether to dump compressed or not. A minimum of
five processors and more than 2GB of memory is required for the system to take a compressed
dump.
NOTE More than one crash may occur at the same time. In such cases, the dump
taken is uncompressed and the following message is displayed.
*** Dump defaulting to sequential without compression
*** Recursive Crash.
After a system crash, before dump starts, the dump type can be changed to compressed or
uncompressed from the console.
During compressed dump, dump progress is updated on the console every 15 seconds.
When savecrash (see the savecrash (1M) man page) runs during bootup, the dump is copied
on to the file system. savecrash copies compressed dump faster since the dump size is
smaller compared to uncompressed dump. The -p option, used with savecrash can be used to
avoid saving portions of the dump from dedicated dump devices. The -z option, used with
savecrash is ignored since the dump is already compressed. Specifying a chunk size lesser
than the size of memory belonging to one compression unit for compressed dump is also
ignored.