Time Capsule and other network storage appliances are becoming very popular for providing shared "personal cloud" storage. Naturally, this storage looks very appealing as a backup destination. The thought of backing up all of your stuff without having to plug in a cable is very alluring. Indeed, this storage is well suited for the sharing of media files, but there are some logistical and practical hurdles to backing up large amounts of data, as well as backing up macOS system data to these devices. There are also some logistical hurdles to restoring a full system backup from a network volume. Below we explain how to back up macOS system files to a network volume, then we describe some of the limitations and performance expectations of this solution.
Note on bootability: You cannot boot your Macintosh from a backup kept on a network volume. If you require a bootable backup or if you ever need to restore system files, you must use an external hard drive enclosure attached directly to your Mac to create a bootable backup.
As described in this section of the documentation, CCC will only back up system files to or from locally-attached HFS+ or APFS filesystems. To meet this requirement, you can ask CCC to create a disk image on your destination network volume. A disk image is a single file that contains the contents of another hard drive. When you double-click on a disk image file, the disk image's volume is mounted locally, as if it were an external drive attached directly to your Mac. To back up to a disk image with CCC:
- Choose your source volume from the Source selector.
- Select New disk image... from the Destination selector.
- Unless you're making an archival backup of your data, choose the option to create a read/write sparse bundle disk image file*.
- Specify the location where you want to save the disk image file. You will find your network volume in the sidebar of the New disk image save dialog**.
- When you click the Clone button, CCC will create a disk image on the backup volume, back up the specified data, then unmount the disk image when the task is complete.
* If that option is unavailable, choose the option to create a sparseimage file instead. Note, however, that some NAS devices cannot accommodate large sparseimage disk images. Sparseimage disk images are monolithic files, and some NAS devices may impose a 4GB or 2TB file size limitation, which will limit the amount of data that you can back up to a disk image. CCC does not support the creation of sparseimage disk images larger than 2TB.
** Instructions for gaining access to network volumes is available in the macOS Help Center. If your network volume does not appear in CCC's Source or Destination menu, consult the documentation that came with the storage device you are trying to access, or choose "Help Center" from the Finder's Help menu ("Mac Help" on Yosemite and above) and search for "connecting to servers".
"Convenient" and "fast" often go hand-in-hand, but that often isn't the case when backing up to a network volume. There are several factors that can greatly reduce the performance of your backup, and this backup strategy involves several of them. If you're finding that your network backups are slow, consider our network backup troubleshooting suggestions.
There are some logistical challenges to restoring a full system from a disk image backup. In particular, you must have some other installation of macOS that you can boot from in order to perform the restore — you can NOT boot from your disk image backup on the Time Capsule or other network device. Before you have to rely on your backup in a catastrophe, prepare yourself for this logistical challenge. Learn more about this in the Restoring from a disk image section of the documentation.