Time Machine, or “backups for the rest of us,” is very different from traditional file-totape backups, and a very powerful backup system that can store multiple versions of files. Unquestionably, Time Machine is an impressive way to back up. Its simple interface masks a complex system underneath, only some of which is appropriate to go into in depth here.
Time Machine is nontraditional and rather unconventional at times. It makes backup effortless for the end user and smaller environments, but needs to be evaluated by system administrators for any scenario involving more than five users or a certain threshold of data. Administrators need to account for how Time Machine differs from other backup methods when planning for system backup.
Time Machine works well in home settings, where typically fewer computers than in office environments back up to any given destination. Time Machine can back up to locally attached or network storage.
Much of Time Machine’s power comes from its use of Leopard’s fsevents API. fsevents allows Time Machine to be informed of changes on disk rather than having to scan an entire volume for changes against another list. As an administrator, you should consider several things before deciding whether to use Time Machine as a backup mechanism.
These include limitations on what administrators can control, Mac OS X Server, behavior and event handling, rotation of backup media, and backup of FileVault-protected homes. Unlike most systems that administrators work with, Time Machine requires little to no configuration or maintenance.
However, the downside is that system administrators have little that they can control. On its own, Time Machine will back up once an hour to the destination configured in the Time Machine Preference pane. The destination can include networkmounted storage on an Xserve or other appropriate Apple Filing Protocol (AFP) device.
Time Machine may not be a good strategy for Mac OS X Server. On Mac OS X Server, Time Machine backs up only servers running in standard or workgroup mode. Time Machine does not allow for rotation of backup media. In other words, you can choose only one destination in the Time Machine Preference pane:
– If this destination is a locally attached disk, it cannot be removed and taken offsite, or easily substituted for another.
– If the destination is a server, however, the server’s backup share can then be backed up.
– If the destination specified is a network share, a disk image per client is created on the share point and used repeatedly. This configuration allows many clients to back up to the same share point, but may increase network traffic and slow user connections.
Last but not least is one serious drawback for mobile users: Time Machine backs up FileVault-protected home systems only when the associated user is not logged in. A warning appears if Time Machine, when enabled, detects any FileVault home system that is logged in.
It may be undesirable to have a backup system that works only when users are logged off. Some companies may require encrypted home directories. Plus, Mac OS X is designed to be able to run long periods of time without logging out or rebooting.