Installation manual

Small Capacity System Disks
H.5 Managing Single or Small System Disk Systems
H.5 Managing Single or Small System Disk Systems
The primary goal for this type of environment is to reduce the system disk block
usage incurred by the OpenVMS VAX system during normal operation. Both
dynamic usage and static requirements can be reduced in various ways. Some
system processing overhead can also be reduced or eliminated in this manner,
along with a corresponding reduction in system disk I/O.
H.5.1 System Dump File
One of the best mechanisms for reducing the total block overhead of the system is
to carefully define the usage of the system dump file. Normally, this is configured
as a separate file, SYS$SYSTEM:SYSDUMP.DMP, to which the contents of
memory are written after a detected system failure. Depending on your system
requirements, you might be able to reduce or eliminate this disk usage.
One effective technique is to use part of the system paging file,
SYS$SYSTEM:PAGEFILE.SYS, as a temporary dump file, so that the space
used for dump files is not permanently reserved and gets used only in the
event of a crash. To do this, you need to modify some system parameters in
SYS$SYSTEM:MODPARAMS.DAT and delete the actual SYSDUMP.DMP file
if it exists. This method is most effective for systems having small or medium
memory sizes.
Alternately, you might set the DUMPSTYLE parameter to use the selective dump
mechanism to reduce the size of the dump file. This method is typically used for
large memory systems that do not need to preserve the entire memory contents
in the event of a system failure. Instead of using selective dumps to the paging
file, keep a separate, but smaller, SYSDUMP.DMP file.
If you have no need to preserve dump files or are running in a very stable
environment, you might want to clear the DUMPBUG parameter to avoid all
dump processing and not write a dump file on failure.
H.5.2 Using PAGEFILE.SYS for the Dump File
To use the system paging file as a dump file, add the following lines to the
SYS$SYSTEM:MODPARAMS.DAT file:
DUMPBUG = 1 ! Enable system dumps (default)
SAVEDUMP = 1 ! Keep dump in pagefile until analysis
DUMPFILE = 0 ! Disallow AUTOGEN to create or size dump file
Then delete the SYSDUMP.DMP file by entering the following command:
$ DELETE SYS$SYSTEM:SYSDUMP.DMP;*
Because the system currently has the file open, the delete command does not
physically remove the file until the system is shut down and rebooted. Use
the AUTOGEN facility to reboot the system. When it has rebooted, enter the
following command to clean up and finish the deletion of the file (and any others
that were in a similar state):
$ ANALYZE/DISK/REPAIR SYS$SYSDEVICE:
After a system failure that writes dump information to the page file, you can
analyze the data by entering the following command:
$ ANALYZE/CRASH SYS$SYSTEM:PAGEFILE.SYS
Small Capacity System Disks H–7