Take Control of Mac OS X Backups: Part Two

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Editor’s Note: The following article is an excerpt from Take Control of Mac OS X Backups (version 1.1), a $10 electronic book available for download from TidBits Electronic Publishing. In part one, Joe Kissell covered the different approaches you can take for setting up a backup strategy featuring duplicates and archives. Today’s installment looks at when to schedule backups, how many backups you need, and how to backup a small network.

Scheduling Backups

I can say from personal experience that backups are far more likely to happen regularly if your backup software runs automatically on a schedule. And let me be quite clear: regular backups are the only kind that matter. I think it’s fair to state this as a corollary to Murphy’s Law: “The likelihood of suffering data loss increases in direct proportion to the elapsed time since your last backup.” In other words, if you’re performing all your backups manually, the one day you forget (or run out of time) will be the day something goes wrong.

One consideration in choosing a backup schedule is media management. For example, if you’re backing up to a recordable DVD, you must be prepared to insert a blank disc whenever the schedule runs. Swapping media can be an intrusion into your normal routine (especially if that routine involves the frequent use of other discs in the drive you use for backups). On the other hand, if you schedule backups to run when you’re not around, you must always think ahead and make sure the drive has the necessary media ready. If, on the other hand, you’re backing up to a hard disk or network device that can stay connected all the time, this problem occurs less frequently, if at all.

Depending on the speed of your computer, which software you use, and how you configure it, you may find that your computer slows down significantly while backups are running. This could be an argument for scheduling backups for when you’re not using the machine. However, if you do not leave your computer on all the time, you will need to take special care to ensure that it’s on and ready when the backups are scheduled to run.

How often should you back up your computer? And if you’re making both duplicates and archives, how often should you update each?

No single answer is right for everyone, but as a starting point, my rule of thumb is that duplicates should be updated at least as frequently as major changes to your system (such as installing Mac OS X updates or new versions of applications), and archives should be updated every day you make minor changes (receiving e-mail, modifying text documents, and so on). Thus, if you use your computer heavily every day, and often install new or updated software, you might opt for weekly updates of your duplicates and daily updates of your archives. On the other hand, if you use your computer only occasionally, the schedule could become once a month for duplicates and once or twice a week for archives. Under no circumstances do I suggest backing up less frequently than once a month or more frequently than twice a day—the risk is too high in the former case and the aggravation too great in the latter.

( Tip: Always update your duplicate just before installing system software updates. That way, if the new version of the software contains any serious problems, you can easily roll back your system to its previous state.)

There may be some cases in which you could not afford to lose even a half-day’s work in the event of a serious problem, making twice-daily archives seem inadequate. If you’re working on an important document, there’s nothing wrong with copying it to another volume once per hour or as often as you feel it’s necessary—or scheduling your backup software or a synchronization utility to do so for you. But updating an entire archive that frequently is likely to slow down your work.

Keeping Multiple Backups

A sound backup strategy always includes backups of your backups! Picture this: you’ve diligently backed up your computer’s internal hard disk to an external drive. Then one day, lightning strikes and both drives are damaged—or your home is robbed and all your equipment stolen. So much for your backup. Backup media can fail for all the same reasons your hard drive can fail. So having just one backup, in my opinion, is never enough. You should alternate between two or more sets of backup media for greater safety. If you’ve set up your backups to run on a schedule, this might mean using set A (a hard drive or a stack of CDs) every day for a week, then switching to set B (a different drive or stack of CDs) for each day of the following week, then switching back—and so on.

So are two sets enough? It depends. Most experts recommend using at least three sets, of which one is always stored off-site. But this advice was first given in the days when the media commonly used for backups was much less reliable than what’s available today. And the cost of three sets of media—especially if you’re talking about hard drives—can be hard to swallow for the average home or small-business Mac user.

In my opinion, except for mission-critical business use, two sets each of duplicates and archives should be adequate for most users. If you back up to hard drives, this can mean two drives, each of which is partitioned to store both a duplicate and an archive. Of course, if you can afford a third set, your data will be somewhat safer—and your backup routine will be somewhat easier. In any case, you certainly should keep one of those sets in another location all the time.

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