Several services also let you back up any network-mounted volume that's available via the Desktop. Flat-rate services except CrashPlan won't let you back up such volumes; iDrive, JungleDisk, and SpiderOak allow it. Jungle Disk and SpiderOak require that you navigate to the /Volumes directory to reach networked drives, a seemingly unnecessary step instead of showing those drives as available sources.

The idiosyncrasies really show when it comes to choosing files to back up. Backblaze only lets you select drives, and relies on an exclusion set up to remove items from the backup. By contrast, Jungle Disk has extraordinarily finely detailed settings and choices for both selection and exclusion. Several packages let you avoid backing up files above a certain size, too, which would let you exclude large files to avoid or ones that you archive elsewhere, such as movies and virtual disk images. Jungle Disk also lets you select files by wildcards and file type.

Mozy appears to be unique in using Spotlight both for preset selection options (such as all your applications' preferences) and allowing new selections based on a Spotlight search.

Excluding files is tedious in most programs. Almost all of the software we looked at uses a hierarchical selection method to choose a folder and all nested folders; some use a Mac convention of clicking on triangles to expand or collapse a nested item, others plus and minus signs. To exclude a nested item, you may have to click down several levels in some packages, find the item, and uncheck a box next to it.