Backup, Recovery, and Troubleshooting
Backup and recovery on OpenVMS centers on BACKUP and the save-set format. Know the difference between an image backup (saves the entire volume, preserving file structure) and a file-level backup (saves selected files). BACKUP can write to tape or disk, and restore uses the same utility. Understand incremental and journal-based strategies, and that a save set carries its own directory structure. Candidates should know that BACKUP /IMAGE is used for system disks and that a restore of an image backup can recreate a bootable volume.
Troubleshooting methodology: gather symptoms (SHOW SYSTEM, SHOW DEVICES, error logs via ANALYZE/ERROR_LOG), isolate the layer (hardware, file system, network, application), and use the appropriate tool. Know ANALYZE/DISK_STRUCTURE for file-system consistency, ANALYZE/ERROR_LOG for hardware errors, and the operator log (OPCOM) for system events. Recovery from a crash may require booting from alternate media, running file-system checks, and restoring from backup.
Traps: assuming a file-level backup can restore a bootable system disk (it cannot, in general); confusing BACKUP's /IMAGE with a physical disk copy; and forgetting that a save set must be mounted/selected correctly before restore. Also know that a failed boot may be due to a corrupt system disk, a bad parameter file, or a missing startup file.
Rule of thumb: for disaster recovery, keep an image backup of the system disk plus regular file-level backups of data; test restores, because an untested backup is not a backup.