Versioning

You can always achieve some kind of version retention with most any backup software. For example, if you perform a full backup every night onto seven different discs, one for each day of the week, then you will have access to different versions of files you've been working on during the last week.

As usual with backup software, however, a simple concept can be made much more convenient for the user -- and therefore more likely to be used. In the context of file-based backup software, my definition of "versioning" means "the ability to automatically retain the last N versions of any file".

Versioning for Accidents

Versioning is not targeted so much at catastrophes like hard disk failure, but more at human error. The classic example is document editing. I'm editing a big report and, on Monday, the boss says it no longer needs to cover our California branch, so I delete that part. Unfortunately, on Wednesday, the boss sticks his head in and says he made a mistake -- the report does need to cover our California branch after all. I've closed my editor several times since I made that deletion, so there's no way I can just "undo" my way back to the Monday version of the report.

Versioning is tailor made for this kind of problem. With versioning, I just ask my backup software to show me all the versions it has retained of my report. By looking at the timestamp on each, I can quickly locate one that contains the section that I need to recover.

Note that per-file versioning can be much more effective than just keeping versions of entire backups. If you retain the last seven daily full backups, you can only "see" seven days into the past. But if you can tell your backup software to retain the last seven versions of any changed files, there's no telling how far back in time that might represent. For example, if there's a file that you change only once per month, then you would be able to "see" seven months into the past.

Shopping for Versioning

Versioning is a feature that is definitely not available in all low-end backup software. However, it is available in some inexpensive packages, and it can be invaluable for many users.

Versioning is usually a per-file feature, so it's worth mentioning that it doesn't work so well for email. Email software (such as Outlook) typically stores messages (roughly speaking) in one big file, not one file per message. Thus, versioning usually doesn't make it easy to get back a previous version of an email message you've been drafting, or recover a particular deleted message.

Differential and Incremental BackupsSoftware Buyer's Guide