4 Disk Compression (DCOM)
The Disk Compression (DCOM) utility moves disk file extents to yield more usable space on a disk.
You can use DCOM to:
•
Analyze the current space allocation on a disk
•
Relocate file extents on a disk
•
Reduce the number of free-space extents, which reduces the effort needed to allocate or
deallocate space
•
Combine free space into larger extents so that files can be allocated with larger extents, which
decreases the incidence of file-system error 43, (unable to obtain disk space for file extent).
Although this decreases the incidence of file-system error 43 it does not guarantee elimination
of this error.
NOTE:
DCOM does not compress audit-trail files because the TMF must maintain exclusive access
to these files for update purposes. However, DCOM does compress audited files.
DCOM supports 512-byte disks and 514-byte disks.
Page
Topic
(page 83)
Security
(page 83)
DCOM Syntax
(page 85)
Handling SMF Files
(page 85)
Exiting DCOM
(page 85)
Stopping DCOM
(page 85)
Completion Information
(page 86)
Guidelines
(page 88)
Examples of Compression Output
(page 89)
Changing the Default Work File Volume
Security
DCOM is privileged, and each customer must determine which users are allowed to run it. To
control access to DCOM:
•
Do not license DCOM's program file for general use. Without licensing, only the super ID
(255,255) can run DCOM.
•
License DCOM's program file and limit access to a subset of users by either setting file security
attributes or using a Safeguard access-control list.
When determining security, be aware that DCOM improves system performance after it finishes.
However, while DCOM is working, it can have a slight negative impact on system performance
and should be restricted to system operators.
To set the appropriate level of access to DCOM and other system utilities, refer to the security
policy established by your organization. For more information about securing information on the
NonStop operating system, see the Security Management Guide.
DCOM Syntax
DCOM is noninteractive, and it can be run online while the disk is operating. It displays reports
and messages at the home terminal (by default), or sends the output to the file specified in the OUT
run-option.
Security
83
