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Cloning a Time Machine backup |
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Can I use Carbon Copy Cloner to clone my Time Machine backup?
For important, albeit technical reasons, Carbon Copy Cloner will usually avoid backing up a Time Machine backup set. It is possible, however, to clone a Time Machine volume with CCC when the following conditions are met:
- The target volume is of equal total capacity or larger than the Time Machine volume
- Both the target volume and the Time Machine volume can be unmounted
- You have selected the "Backup everything" cloning method in CCC
- You have checked the box to "Delete items that don't exist on the target"
When these conditions are met, CCC will proceed with a block-level clone of your Time Machine volume. If these conditions are not met, CCC will proceed with a file-level copy and will exclude your Time Machine backup from the backup task. If you don't see "Block copy" in the title of the cloning console window, click the "Stop" button to abort the clone and consider an alternative approach. You can learn more about the "Backup everything" cloning method in the "Backing up everything: The venerable Full Volume Clone" section of the documentation
Do you really need to clone your Time Machine volume? After all, it is a backup...
If the only thing that your backup drive is used for is Time Machine, you could just start "fresh" on the new volume. We recommend that you keep the old drive around for a few weeks in case you want to retrieve a file modified in the backup window of your previous Time Machine backup, but a fresh start is a full backup.
The technical reasons for excluding a Time Machine backup from a file-level copy
Time machine uses a feature of the HFS+ filesystem that was introduced in Leopard called "directory hard links". Like file hard links, a directory that is hard linked to another directory is not actually a new directory, it is simply a pointer to the previous directory. Time Machine uses these hard links to make references to entire directory trees whose contained files have not been modified. To properly clone a Time Machine backup, these directory hard links must be preserved.
Directory hard links are proprietary to Apple. Apple discourages their casual use by third party developers because, used incorrectly, they could create devastating looping directory structures that would render a volume useless. For this reason and others, support for directory hard links has not been implemented in CCC's file-level synchronization engine. CCC's block-level cloning engine, on the other hand, does preserve directory hard links, and is therefore capable of cloning a Time Machine volume.