Joe’s Recommended Strategy
What I recommend for most users is a two-pronged approach: periodically scheduled (say, weekly) duplicates of your entire hard disk, and even more-frequent (say, daily) archives of your data files.
The duplicates will provide you with a complete, bootable copy of your hard disk, while the archives will pick up all the files that change regularly.
Duplication Strategy You should create duplicates (onto hard drives, ideally) of your primary disk and any other startup volume you normally use. If you have a single, unpartitioned hard disk, then you have only a single volume to worry about. If you have multiple partitions (or multiple internal or external hard drives) that contain bootable systems, I recommend making duplicates of all of them . If a hard drive fails, after all, it can take with it all the partitions it contains; and a disaster that wipes out a single drive could wipe out all of your drives.
Most duplication software enables you to deselect individual folders you wish to exclude from a duplicate; some use selectors, exclusions, or both. Although you could make an argument that some files are not worth including in a duplicate (such as the cache files located in ~/Library/Caches), the safest and most reliable tactic is simply to include everything. A file or folder that seems irrelevant to you may turn out to be crucial to the functioning of your system.
Archive Strategy The archives you create should include all your important files (on each volume you use regularly, if you use more than one). The main question, though, is how you determine which files those are.
Some people suggest performing a full archive—that is, archiving every single file on your disk, just as you do when creating a duplicate. Others suggest performing a selective archive that includes only user-created data files, especially those that change frequently.
With a full archive, you have yet another copy of all your files besides your duplicates—an extra insurance policy. Restoring a full archive onto an empty disk requires fewer steps, and less time, than restoring a selective archive (since in the latter case, you must restore a duplicate first). On the other hand, a full archive requires significantly more storage space, increasing your media cost, and takes longer to run. In addition, some backup software does not enable you to restore an archive as a bootable volume. My own preference is for selective archives, though I would not discourage you from performing a full archive if resources permit.
If you do choose to archive selectively, a good starting place is your home folder. By default, this folder contains most of your preference files, the files shown on your Desktop, and data for many of Apple’s applications (Address Book, iCal, iTunes, iPhoto, Mail, Safari, and so on), among others. Although you can organize your hard disk however you want, Apple encourages you to keep all your user-created documents in the ~/Documents folder or elsewhere within your home folder. So it could be that all your important, user-specific data files exist somewhere inside your home folder—and if not, presumably you are aware of the locations of folders you’ve created elsewhere.
But even if you have assiduously colored within the lines and kept all your personal data in your home folder, should you archive the whole thing? In some cases, the answer is no.
Because Apple designed the home folder as a catchall, it has the tendency to swell to enormous sizes. For example, if you maintain the default settings in iDVD, iMovie, iPhoto, and iTunes, all your digital media will be stored in your home folder. If, like me, you’ve imported your entire collection of CDs into iTunes, you may be looking at a huge Music folder (mine is well over 16 GB, and that is small compared to some). If you store digital video on your computer, your Movies folder will certainly be even larger.
Although there’s nothing wrong with adding all those files to your archive, it may not be strictly necessary either—because all those files should already be backed up safely as part of the duplicates you maintain. If, as in the case of imported CD tracks, digital photos, or video downloads, you modify those folders less frequently than you perform duplicates, you might consider saving time and space by excluding them from archives. But if in doubt—especially when it comes to irreplaceable photos and video—err on the side of including them; having an extra backup just may save your bacon one day. Purchases from the iTunes Music Store also require special handling; see the sidebar on the next page.
Besides digital media, you may wish to manually exclude certain other files from an archive, if needed to save space. For instance:
• Downloads: Applications and other files you’ve downloaded from the Internet can nearly always be downloaded again. It may not be worth dedicating significant media space to hold such files.
• Cache Files: Temporary cache files, such as the ones stored in ~/Library/Caches, are not crucial to an archive, as they will be recreated automatically if needed.
Having determined what you need to back up and how often, you’re ready to make decisions about what hardware you will need.
[ Joe Kissell is the author of several books about Macintosh software, including Take Control of Spam with Apple Mail ( Tidbits Electronic Publishing, 2004) and curator of Interesting Thing of the Day. ]