Mac OS X Time Machine backup disk

Time Machine is the backup application available with Mac OS X.

Tivoli® Storage Manager can be used at the same time as Mac OS X Time Machine application. However, due to the unique nature of how the Mac OS X Time Machine application backs up data, consider the following items before using Tivoli Storage Manager to back up the Mac OS X Time Machine data:

• The Mac OS X Time Machine backup disk makes extensive use of both file and directory hard links to minimize disk usage. For example, if the disk backed up with the Mac OS X Time Machine application is 5 GB, the first backup copies 5 GBs of data to the Mac OS X Time Machine backup disk.

  Subsequent backups only copy the files that have changed since the previous backup. All files and directories that have not changed are hard-linked with the version that was copied during the previous backup.

  The Finder shows each backup as 5 GB, for a total size of 10 GB. However, because of the use of hard links, the total disk usage is only slightly larger than 5 GB.

  All hard-linked objects that are not already on the Tivoli Storage Manager server are backed up.

  For example, 10 GB of data would be sent to the Tivoli Storage Manager server.

• When files that are restored are hard-linked, Tivoli Storage Manager recreates the original hard link. Recreating the original hard link can only be done if all files that are hard-linked are restored at the same time. Restoring all the hard-linked files at the same time is not a practical method for a large backup disk that uses the Mac OS X Time Machine application.
• When the Mac OS X Time Machine application copies files to the backup disk, ACLs are added to the files to protect them from deletion. Tivoli Storage Manager can back up and restore files with ACLs. However, any files that are restored must have these restrictive ACLs in place.

Tip: For best results, exclude the Time Machine application backup data. All Time Machine application data is in a directory named Backups.backupdb.