Time Machine (software): Difference between revisions

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'''Time Machine''' is an automated backup application, created by [[Apple Inc.]] and distributed with [[Mac OS X]]. It creates hourly incremental backups to an external drive or over the network.
'''Time Machine''' is an automated backup application, created by [[Apple Inc.]] and distributed with [[Mac OS X]] 10.5 Leopard. It creates hourly incremental backups to an external drive or over the network.
 
==How it works==
Every hour, a daemon process mounts the backup volume (a HFS+ formatted sparse disk image), scans the filesystem for changes, and backs them up. Changes are detected via the ??? interface which was introduced in Leopard; when there is no information available, the backup process does a full filesystem scan.
 
For each backup, a new directory tree is created on the backup volume, mirroring the current state of the filesystem. Modified files are added incrementally; non-modified files are hard-linked from the previous successful backup tree. Whole directories that are not modified are hard-linked at the directory level (directory hardlinks are a new feature introduced by Apple in the HFS+ filesystem).
 
After a successful backup, some old backups may be purged. The goal of the purge process is to keep no more than: hourly backups of the last 24 hours, daily backups of the last week, and weekly backups for as long as there is space left on the backup volume.

Revision as of 04:05, 23 May 2008

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Time Machine is an automated backup application, created by Apple Inc. and distributed with Mac OS X 10.5 Leopard. It creates hourly incremental backups to an external drive or over the network.

How it works

Every hour, a daemon process mounts the backup volume (a HFS+ formatted sparse disk image), scans the filesystem for changes, and backs them up. Changes are detected via the ??? interface which was introduced in Leopard; when there is no information available, the backup process does a full filesystem scan.

For each backup, a new directory tree is created on the backup volume, mirroring the current state of the filesystem. Modified files are added incrementally; non-modified files are hard-linked from the previous successful backup tree. Whole directories that are not modified are hard-linked at the directory level (directory hardlinks are a new feature introduced by Apple in the HFS+ filesystem).

After a successful backup, some old backups may be purged. The goal of the purge process is to keep no more than: hourly backups of the last 24 hours, daily backups of the last week, and weekly backups for as long as there is space left on the backup volume.