More than two dozen third-party backup apps can make bootable duplicates. (You can see a list in the online appendix to my book Take Control of Backing Up Your Mac.) It's also possible (if not especially convenient) to clone a drive using Disk Utility or by using the diskutil command in Terminal. Most of these apps and processes do an entirely respectable job, but two cloning utilities — Shirt Pocket's $28 SuperDuper and Bombich Software's $40 Carbon Copy Cloner — stand above the rest. Each has a long history, focuses on cloning, presents a simple and clear user interface, and includes unusual features that make it an especially good choice for creating and maintaining bootable duplicates.
SuperDuper and Carbon Copy Cloner
For everyday cloning tasks, SuperDuper and Carbon Copy Cloner are equally good in almost every respect, and they have a core set of features in common. In both apps, you choose a source drive (say, your startup volume) from a pop-up menu on the left, a destination drive (your clone-backup volume) from a pop-up menu on the right, and any desired options using additional pop-up menus or buttons. Each utility provides a plain-English summary of what's about to happen; you then click a button to begin the copying operation.
Both apps give you the option to erase the destination before copying files from the source; or to update your clone incrementally to reflect only those files that are new, changed, or deleted since the previous cloning run. (The free trial version of SuperDuper disables the incremental update feature, which Shirt Pocket calls Smart Update.) Both also let you deselect specific files, folders, or filename patterns to omit them from your backup, although they have very different interfaces for doing so — I find this task much easier to accomplish in Carbon Copy Cloner than in SuperDuper.
In addition to using an actual drive as the destination, each app can copy the source volume to a disk image (which won't itself be bootable, but which can be restored to a drive that will then become bootable); you can choose from among several disk-image formats, with or without compression. Carbon Copy Cloner also offers encryption for disk images, while SuperDuper lets you choose from three levels of compression. Likewise, you can use either app to restore a drive from a disk image. Both apps also let you schedule backups to run unattended — on a recurring schedule, when the destination drive is mounted, or both. (For example, I update my iMac's clone twice a day, since its destination drive remains connected all the time, but my MacBook Pro's clone updates only when I plug in my backup drive.)
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