What it means is that a block copy copies everything in a data block from one device to the other. The results are almost an exact copy of the original.
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A file copy, on the other hand, copies data file by file, and while the file data remains the same, the location of the file on the source and destination devices will likely be very different. Using a block copy is faster, but it does have some limits that affect when it can be used, the most important being that copying block by block requires that both the source and destination devices be first unmounted from your Mac.
This ensures that block data doesn't change during the copy process. But it does mean that neither the source nor the destination can be in use when you use the Restore capabilities. If you need to clone your startup drive, you can make use of either your Mac's Recovery HD volume or any drive that has a bootable copy of OS X installed.
We'll provide information about how to use the Recovery HD Volume to clone your startup drive, but first, we'll look at the steps in cloning a non-startup drive attached to your Mac.
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The Disk Utility app will open, displaying a single window divided into three spaces: a toolbar, a sidebar showing currently mounted drives and volumes, and an info pane, showing information about the currently selected device in the sidebar. If the Disk Utility app looks different from this description, you may be using an older version of the Mac OS. The volume you select will be the destination drive for the Restore operation.
A sheet will drop down, asking you to select from a drop-down menu the source device to use for the Restore process. The sheet will also warn you that the volume you selected as the destination will be erased, and its data will be replaced with data from the source volume.
Use the drop-down menu next to the "Restore from" text to select a source volume, and then click the Restore button. The Restore process will begin. A new drop-down sheet will display a status bar indicating how far along in the Restore process you are. You can also see detailed information by clicking the Show Details disclosure triangle. Click Done to close the Restore sheet.
Carbon Copy Cloner CCC is great because it's easy to configure, it gets the job done quickly, and you can pretty much set it and forget it.
Cloning a disk can be as simple as selected a source disk and destination—whether that destination is another hard drive, a disk image, or a network share. From there you just click the "Clone" button and CCC does all the work.
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If you don't want to backup an entire drive, however, CCC can handle incremental and partial backups as well. It can also sync files between two drives, and you can choose to archive old or deleted files or just keep the backups completely identical. If you want your disk cloning and backups to be almost completely hands-free, you can schedule backups or tell CCC to start the backup process when a specific disk is connected to your machine.
Basically, whatever you need it to do it can handle and it will get the job done fast and easy. CCC really has no downsides. Unless you like the crazy interface and restore features of Time Machine, or prefer something with a more simplified online backup option like Crashplan or one of these syncing file services , maybe you'll want to try something else.
But CCC can backup to drives anywhere on else on the internet and you can use backups to restore old versions of files—just not as elegantly as you might with other software. Everything it does it does well, so there's little to complain about. The main issue we now have with Carbon Copy Cloner is its price. It's still our favorite app, but we'd like to see it somewhere around half the price. The upside, however, is you can still download the older version for free. While it isn't supported in Mountain Lion, it appears to be working fine.
This may not be the case forever, but for now it it isn't a problem.