Unix Backup and Recovery

Volume Verification

Another often-ignored area of backup and recovery software is its ability to verify its own backups. There are plenty of horror stories out there about people who did backups for years or months assuming that they were working just fine. Then when they went to read the backup volumes, the backup software told them that it couldn’t read them. The only way to ensure that this never happens to you is to run regular verification tests against your media. There are several different types of verification:

Reading part of volume and comparing it

There is at least one major vendor that works this way. If you turn on media verification, it forwards to the end of the volume and read a file or two. It compares those files against what it believes should be there. This is obviously the lowest level of verification.

Comparing table of contents to index

This is a step up from the first type of verification. This is the equivalent of doing a tar tvf. It does not verify the contents of the file; it verifies only that the backup software can read the header of the file.

Comparing contents of backup against contents of filesystem

This type of verification is common in low-end PC backup software. Basically, the backup software looks at its backup of a particular filesystem, then compares its contents against the actual contents of the filesystem. Some software packages that do this will automatically back up any files that are different than what’s on the backup or that do not ...