Chapter 6: Backup

Overview

OpenVMS has the capability to:

• Back up and restore individual files, directory structures, and whole disks, including the system disk (complete with boot records).

• Back up and then immediately verify the results against the original files.

• Incrementally back up files that changed or are new since the last full backup.

• List file names in the backup container (called a save set).

• Support disk-to-disk, disk-to-tape, and tape-to-disk backup and restore operations.

• Support disk-to-disk copy operations.

• Perform all of these operations on shadowed disks.

• Use the Save Set Manager (SSMgr) to keep track of backup save sets.

Unlike UNIX, one disk backup program, BACKUP, is available in OpenVMS. The BACKUP program will perform disk copy, disk backup, and disk restore functions. The backup destination can be either another disk or tape. BACKUP will support other media as well, but only tape and disks are practical because of their capacity. For instance, a CD or DVD could be used as backup media. An entire disk can be copied, a subdirectory tree and files, or only those files that changed since the last backup can be saved. This latter operation is called incremental backup. The backed-up data is not compressed, but, depending on the device and BACKUP options, a BACKUP-generated checksum in the form of a cyclic redundancy check (CRC) accompanies the data files to aid in media error recovery. Active CRC is the default, but it can be turned off with the /NOCRC qualifier. Most modern tape drives operate in compression mode and / or CRC mode by default. Permitting BACKUP to compute the CRC as well is like having both suspenders and a belt to hold up your pants.