|  |  | # A closer look at how CCC determines the "bootability" of a destination volume
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CCC determines whether your destination volume will be bootable and indicates any configuration concerns in the "Cloning Coach" window. If you see a yellow warning icon next to the "Customize these settings" button, you can click on that icon to see these concerns. CCC will also present these concerns to you the first time that you back up to any particular destination volume.

If CCC doesn't raise any configuration concerns, and the destination volume has an OS on it when the backup task is completed, and barring any hardware problems that might interfere, your backup volume *should* be bootable.

## Configuration concerns that affect bootability of the destination volume

CCC looks for the following configurations to determine if a destination volume will not be bootable:

- The destination volume cannot be a disk image -- you cannot boot your Macintosh from a disk image.
- If the Macintosh is a PowerPC Macintosh, the destination device must be an internal volume or on a Firewire hard drive. Intel Macintoshes can boot from either an internal volume, a Firewire hard drive, or a USB hard drive.
- The files and folders required by OS X must be present on the source volume. These include: /Library, /System, /bin, /etc, /mach_kernel, /private, /sbin, /tmp, /usr, and /var.
- The files and folders that are required by OS X must be selected to be copied to the destination volume (applicable only to the "Incremental backup of selected items" cloning method).
- If the Macintosh is a PowerPC-based Macintosh, the hard drive on which the destination volume resides must be partitioned using the APM (Apple Partition Map) partitioning scheme. Intel-based Macintoshes ship with hard drives formatted with the GPT (GUID Partition Table) format, and will not boot a PowerPC Macintosh.
- If the Macintosh is an Intel-based Macintosh, the hard drive on which the destination volume resides must be partitioned using the Apple Partition Map or GUID Partition Table partitioning scheme (CCC will indicate, however, that an APM-partitioned disk is not an Apple-supported configuration for Intel-based Macs). You may have difficulty booting or running an Intel-based Macintosh from a hard drive formatted with the MBR (Master Boot Record) partitioning scheme.
- CCC will issue a warning if the operating system that you're backing up (or restoring) is older than the OS that your machine shipped with.

CCC does not maintain an exhaustive list of hardware:shipping OS pairs. CCC also cannot determine whether the destination will be bootable when the source or destination are remote Macintosh volumes.

Related documentation:

- What makes a volume bootable?
- Don't install older versions of OS X
- Western Digital hard drive enclosures and bootability

## Configuration concerns that affect the preservation of filesystem metadata

CCC will note a concern if there is a compatibility mismatch between the source and destination filesystems. For example, if you are backing up files from an HFS+ volume to a network filesystem, some of the filesystem metadata cannot be preserved. In many cases this is acceptable and you can ignore the message. Each of the possible concerns that CCC might raise are listed below. The "risk" associated with not preserving each type of metadata is explained plainly, so you can decide whether the destination volume will suit your needs.

### The destination doesn't support Access Control Lists

Access Control Lists specify a granular list of the privileges that users and groups have for a particular file or folder (e.g., read, write, get information, delete, etc.). These advanced privilege settings generally apply only to user accounts that have been created on your Macintosh — for example, to prevent other users from deleting items from your home directory. If you are backing up your own files to a locally-attached hard drive, or to a network file share on a trusted computer, the Access Control List filesystem metadata is relatively unimportant. If you are backing up to or from a network filesystem in a business or education setting, however, check with your tech support staff for additional advice on whether this metadata must be preserved.

### The destination doesn't support hard links

A hard link makes a single file appear to be located in multiple places on your hard drive. If a single file had 20 hard links scattered across the disk, each hard link file would consume no additional space on the hard drive, and editing the content of any one of those files would immediately affect the content of every other hard link to that file.

When you back up the contents of a volume that contains hard links, ideally you want to preserve the hard links. If the destination filesystem doesn't support hard links, each hard linked file will be disassociated from the original file and will become a copy on the destination. This won't result in any loss of data, but your backup set will consume more space on the destination than on the source. Hard links are leveraged quite a bit on OS X by the operating system, though they are generally less common among user data.

### The destination doesn't support ownership

File ownership indicates which user account on your Mac has control of a file. The owner of a file can limit access to that file from other users on the same computer. If the destination doesn't support ownership, then the owner of each file copied to the destination will be set to the user that mounted the destination. If the destination volume is accessed elsewhere (e.g. mounted on another Mac or even by a different user on the same Mac), then any restrictions that you have placed on those files may not be honored. If you are backing up files and folders that are not all owned by the same user (e.g. you), you should consider backing up to a local, HFS+ formatted volume or to a disk image instead.

## Some filesystems have file size limitations

Some filesystems have restrictions on how large a file can be. FAT32, for example, limits files to 4GB or less. CCC will proactively warn you of this limitation if you choose to back up a volume whose filesystem supports files larger than 4GB to a filesystem that does not support files larger than 4GB. CCC will then automatically exclude files larger than 4GB from the backup task. Files that were excluded will be reported at the end of the backup task.

If you require that files larger than 4GB are backed up, you must reformat the destination volume with a format that supports larger files.

Related documentation:

- Preparing your backup disk for a backup of OS X

## The destination already has an installation of OS X. Merging a different version of OS X into this destination may cause problems with that installation of OS X

This message appears if you have indicated that files and folders that are only present on the destination should be left alone. While that setting will protect any data that you have on the destination volume that is unique to that volume, it does a disservice to the installation of OS X on your destination.

Suppose, for example, that you have a complete backup of Mac OS 10.6.7 on your backup volume. When you apply the 10.6.8 update to your source volume, many system files are updated, some new files are added, and some files may be deleted. If you use CCC to update your backup volume, but you don't allow CCC to delete the items on the destination that the OS update had deleted from the source, then there will be a bunch of "cruft" left over on the backup volume.

If you should ever need to boot your Mac from your backup volume, these cruft files could cause the OS to behave unexpectedly, and they may prevent it from booting altogether.

CCC can help you perform a clean upgrade or downgrade of OS X on the destination volume by moving items that should be deleted to an archive folder. Any files and folders that you keep only on the destination would also be moved to the archive folder. See the "Protecting data that is already on your destination volume" section of the documentation for more details on these settings.

## Help! My clone won't boot!

See this section of CCC's documentation for troubleshooting advice if you're having trouble getting your backup volume to start your Mac.