The Archive

Sometimes referred to simply as a backup, an archive contains copies of your files as they appeared at multiple points in time. If you want to see the version of a file that existed on your computer 2 weeks ago, an archive can deliver thatalong with today's version and the version that existed a month ago.

An archive starts with a complete copy of all the files in one or more folders. The next time the backup runs, your backup software could make another complete copy, but because most of the files probably have not changed in the meantime, that would use up a great deal of spacenot to mention taking a long time. So backup programs typically perform an incremental archive. This means that on subsequent runs, the software scans the files in the folders you've designated and copies only those files that are new (or newly modified) since the last backup. To be truly useful, archives should also be additive, meaning the backup program adds the new or changed files to the archive without overwriting the files already there. That way, you can retrieve many different versions of a given file, and if you delete it on your hard disk, you can still find it in your archive. Thus, what I refer to as an archive is technically an additive incremental archive.

Synchronization Utilities

Lots of utilitiesincluding several that bill themselves as backup toolsperform synchronization. As the name implies, synchronization means maintaining identical copies of a file, folder, or even an entire disk in two or more locations. Some synchronization utilities can run on a schedule, automatically "backing up" files from a location you specify to another volume. And some can create a bootable duplicate by synchronizing an entire disk to another disk.

There's nothing wrong with synchronizationin fact, it can be incredibly useful in certain circumstances, such as keeping your laptop's hard disk updated with documents you use frequently on your desktop Mac. As a quick and easy way of making an extra copy of certain files, it can serve as a type of primitive backup.

If you want to use a synchronization utility to make duplicates as part of your backup strategy, that is perfectly valid too. However, please do not mistake synchronization for a true backupno matter what the utility's advertising says.

What's true of duplicates is equally true of individually synchronized files and folders: you get only the most recently modified version. You lack the ability to recover an older version of the file, which is a crucial part of a solid backup program. Also, if you don't notice that a file is damaged before synchronizing it to another volume, you may end up with two useless copies. If you synchronize deletions, you lose your insurance against accidentally trashing files. And it's all too easy to accidentally copy data in the wrong direction!

All that to say: a single copy of a single version of your data does not a backup make. By all means, synchronize if you wish, but not as a substitute for proper archives and complete, bootable duplicates.


Some backup programs use the term archive to describe files that have been copied to removable media of some kind for long-term storage and then deleted from the source volume.

Archives sometimes make use of a snapshota list of all the files in the designated folders at the time a backup runs. Even though a certain file may not be copied (because it hasn't changed since the last backup), it will appear in the snapshot list. You can easily see what the entire contents of a folder looked like at various arbitrary points in the past, and restore it to any previous state in a single operation.

After the initial full backup, archives usually take comparatively little time to run, making it easy to back up your data once (or even several times) each day. This ensures that your most recent backup is never more than a day old. Because they also offer tremendous insurance against accidental deletion (or change) and file damage, archives are an essential part of a good backup strategy. But archives alone are not an adequate solution. I say this for two main reasons:

  • Because of the way archives are stored, they do not represent a complete, intact version of your entire hard disk. Ordinarily, an archive is not bootable (at least, not until after you've restored it to a fresh disk). If your main hard drive is completely dead, you won't be able to do any work at all until you've replaced it.

  • It often makes sense for an archive to include only data filesnot your operating system or applications (Archive Strategy, page 105, discusses the pros and cons of such an approach). But reinstalling Mac OS X and applications from their original CDs or DVDs is a lengthy and cumbersome process that you could avoid (or speed up dramatically) with a duplicate of your hard disk.

Archives protect you against inadvertent changes over time, but only a duplicate can get you up and running again quickly after a major problem. In other words, the best backup strategy includes both duplicates and archives.

That said, you can set up both duplicates and archives in many different ways, depending on the hardware and software you have, the types and sizes of files you typically work with, and other variables. I make some general suggestions ahead under Joe's Recommended Strategy (page 104), and I provide more detailed instructions in Chapter 12.

Real World Mac Maintenance and Backups. Industrial-Strength Techniques
Real World Mac Maintenance and Backups. Industrial-Strength Techniques
Year: 2004
Pages: 144 © 2008-2017.
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