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Using Carbon Copy Cloner to backup to and restore from disk images |
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Sometimes backing up your data to a single external hard drive is just too messy and difficult to organize. Suppose, for example, that you have three computers in your household, and everyone backs up to the same firewire hard drive. Where do you put each person's backup? The single hard drive can't maintain multiple operating systems, Mac OS X does not support that. You could split the drive into three partitions, but that isn't very flexible at all. You could clone each person's drive to a folder on the drive, but that's a little difficult to restore from.
A very good solution in a scenario such as this is to use disk images as the medium of your backup. A disk image is a single file residing on your hard drive that contains the entire contents of another hard drive (except for the free space). When you want to access the contents of that filesystem, you double-click on the disk image to mount the disk image as if it were an external drive attached to the machine. Carbon Copy Cloner 3 leverages disk images to provide you the flexibility of storing several complete, bootable* backups on a single shared external hard drive. (* Disk images themselves are not bootable, but you can mount them and restore their content to a physical hard drive to produce a bootable, exact replica of the original).
Backing up to a new disk image
After choosing a source volume from the Source Disk popup menu, choose "New disk image..." from the Target Disk popup menu. Provide a name and choose a location to save your disk image. If you plan to back up to this disk image again in the future, select the option to "Create a read/write sparse disk image". If you want a read-only disk image for archival purposes, choose the option to "Create a read-only disk image". Note that if you schedule a task in which you create a new image, CCC will recreate the image every time the task runs. See the Backing up to an existing (read/write) disk image section below for a more appropriate choice for scheduling backups to a disk image.
Read/write "sparse" disk images
A sparse disk image is a type of read/write disk image that grows as you copy files to it. In general, sparse disk images only consume as much space as the files they contain consume on disk, making this an ideal format for storing backups.
Read-only disk images
When creating a read-only disk image, you have two additional options. If your target disk is short on space, you can compress the disk image. Compression rates vary on the content of your source, but you can typically expect to reduce the size of your disk image by about half when using compression. There is a subtle behavior that you should take note of when considering this option as a space-saving measure: When using the "Incremental backup of selected items" cloning method, CCC will first create a read/write disk image, copy the selected items to it, then convert the disk image to read-only compressed. In this case, you will actually need twice the space on your target as the items to be copied consume on the source. When using the "Backup everything" cloning method, this limitation does not apply, CCC will create a read-only compressed disk image in one step.
The second option allows you to segment the disk image. This option is ideal if, for example, you intend to burn the segments to optical media.* Like with the compression option, CCC will also create a temporary read-write disk image -- not segmented -- when using the "Incremental backup of selected items" cloning method.
* To mount a segmented disk image, all segments must be present on the same media. Burning disk image segments to optical media is a great archival practice, just keep in mind that should you ever need to restore from that backup, you will first need to copy all segments onto a volume with adequate capacity.
Encrypting disk images
If any of the data that you are backing up is sensitive, and if your backup device may be in an insecure location, it is a good idea to enable encryption when backing up to a disk image. CCC uses 128 bit AES encryption to encrypt disk images. Note: CCC does not currently support encryption during scheduled tasks.
Backing up to an existing (read/write) disk image
If you regularly make backups to a disk image, this is the option you will want to choose when choosing a target disk. After choosing a source volume from the Source Disk popup menu, choose "Choose disk image..." from the Target Disk popup menu. In the Open dialog box, navigate to and select your disk image and click the OK button. After clicking on the Clone button, CCC will mount the disk image and backup your data as if it were any other backup device.
When backing up to an existing disk image, be sure to choose a disk image that is writable. If you choose a sparse disk image that CCC created in a previous backup, CCC can be configured to copy everything again, overwriting data on the disk image, or to copy only the items that have changed. A sparse image will grow as data is copied to it.
Learn more about performing basic clones with Carbon Copy Cloner
Learn more about backing up your data with Carbon Copy Cloner
Restoring from a disk image
To restore files or an entire filesystem from a disk image, simply select "Restore from disk image" from the Source Disk popup menu and locate your backup disk image. CCC will mount the disk image and you may then proceed with the restore procedure using either the "Incremental backup of selected items" or "Backup everything" cloning method. If you want to restore your disk image to your boot volume, you will first need to boot from another installation of Mac OS X. Follow these steps before proceeding with the restore procedure defined above:
- Install Mac OS X and CCC onto an external USB or Firewire hard drive
- Boot from that external hard drive and launch CCC
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