Take Control of Mac OS X Backups: The Online Appendixes

In this section, you'll find interesting features that didn’t fit in any of the other categories, but which may be extremely important to you, depending on your needs: compression, encryption, scheduling, and the like. For a description of what a feature means, click any column heading.

Note: The top portion of the table lists programs that offer bootable duplicates, versioned backups, or both. The bottom portion of the table lists other backup, synchronization, and file copying tools. Enterprise-grade software is not shown here.

Last updated: August 14, 2010

Feature Explanations for This Table

Compression: When a backup application compresses your files, they take up less room on your storage media—usually a good thing, as that reduces your costs and lets you store backups for longer periods of time before having to reuse your media. Compression is even more important when data is traveling over the Internet, because compressed data takes less time to send, and online storage costs are often much higher than the cost of local media. On the other hand, compressing files taxes your computer’s CPU, RAM, and disk, and having compressed files may add an extra complication when it comes time to restore data.

Encryption: As long as your backup media is under your physical control, encryption isn’t especially important. But if you store backup media offsite in any fashion, or if anyone else (a thief, say, or a nosy coworker) can get access to your backups, you might prefer that they not be able to see all your data. Some backup software can encrypt all the data on your backup media so that you won’t risk your private information falling into the wrong hands.

Restore Feature: A restore feature simply means that, with a button click or menu command, you can instruct your backup program to return files that you previously backed up to their original location (or better yet, another location). Quite a few programs expect you to simply switch the “source” and “destination” and, essentially, redo your backup. That’s not too bad when you’re restoring all your files or just a single file, but what if you’re restoring a bunch of files from different folders all at once? Wouldn’t you like your backup software to be smart enough to put them all back where they belong, and save you the tedium of manually configuring everything? That’s why a restore feature is a good idea. It’s most important with backup programs that store multiple versions of your files, because otherwise, sifting through a lot of different file versions by hand is going to be a real pain.

Scheduling: Traditionally, most backup programs have used a fixed schedule: you set a time (once a day, twice a week, or whatever—maybe in the middle of the night) and the software does its thing only at that time. For software that uses a fixed schedule, this column lists the most frequent option available (such as once per hour or once per day). Increasingly, though, backup programs offer some form of automatic operation (either by default or as an option), such as backing up files as soon as they change or running in the background every hour. In general, if a program can run once an hour or more frequently and it offers some sort of scanning aid (see just ahead) so that it needn’t do a full scan with each run, you can think of it as being effectively schedule-free. On the other hand, some backup programs don’t support any kind of scheduling—they run only when you activate them manually.

Can Wake Up/Turn On Computer: For backup software that runs on a fixed schedule (once a day, say), it’s handy for it to be able to wake up your computer if it happens to be asleep then, or even turn it on if it’s off. These capabilities, though rare, save you from worrying that a schedule won’t run properly because your computer didn’t happen to be on or awake at the right time.

Scanning Aid: Some programs use Mac OS X’s FSEvents (file system events) framework to find out almost instantly which files have changed since their last run—dramatically reducing the time necessary to scan all your files manually each time your backups run and, in some cases, enabling continuous, real-time backups as your files change. A number of programs watch your file system for changes (“Dynamically detects changed files”) but don’t publicize whether they use FSEvents to do so. And some backup software scans and copies in a single pass, arguably a more efficient approach (depending on your needs) than scanning all your files and then making another full pass to copy them.

Metadata Support: Even though a file may appear to copy correctly, some important information about the file may be missing or incorrect—things like ownership, permissions, modification date, Finder flags, access control lists, and many others (collectively known as “metadata”). Theoretically, backup software should copy every piece of metadata perfectly, though in practice, many types of metadata are so insignificant or seldom used that no harm is done if they’re missing in your backups. Faithful coping of metadata is most crucial when making a bootable duplicate.

I used a tool called Backup Bouncer to test metadata support for as many of these programs as I could. Backup Bouncer checks a great many attributes (though not every kind of metadata), but it divides its results according to how significant the developer feels each one is: “critical,” “important,” and “other.” Instead of listing all the gory details here, I’ve used the Backup Bouncer results to assign a “grade,” as follows:

• A+: The software passes ALL of Backup Bouncer’s tests perfectly.
• A: All “critical” and “important” attributes are copied correctly.
• B: All “critical” attributes are copied correctly, but at least one “important” attribute is not copied correctly.
• C: At least one “critical” attribute is not copied correctly.

Although metadata is in some cases very important, I urge you to take these test results (especially the “C” grade) with a grain of salt, for two reasons. First, because of the way Backup Bouncer groups its results, a fairly insignificant problem can sometimes result in a failed test in a “critical” category. (For example, if a single file were copied with an incorrect Finder label, that would result in a failing grade for the “critical” Finder Flags test, though in real life such an error might not even be noticed, let alone cause any problems.) And second, depending on the way a given backup program is designed and used, it may be irrelevant that certain attributes (such as file ownership) aren’t always copied correctly. And the difference between an “A+” and an “A” is effectively meaningless. So basically: don’t freak if your favorite program gets a less-than-perfect score—but do consider contacting its developer to suggest that they look into using Backup Bouncer to improve its metadata support in the future.

Where you see “Unable to test” in this column, it could mean any of several things: the software may not be compatible with Snow Leopard, which I’m using on my test machine; it may be designed in such a way that it can’t work with Backup Bouncer’s test suite; or I may not have had access to a version of the program suitable for testing.