Getting the most of Mac's new Time Machine backup systemGetting the most of Mac's new Time Machine backup system

Time Machine, the backup software included with Mac OS X 10.5 "Leopard," is one of the highlights of the operating system. I've been using Time Machine for a while, and here are some of my usage tips. Share these with your support staff and employees. Time Machine works much, much better with Mac OS X 10.5.2 than with previous version of Leopard. Be sure to do whatever regression testing is necessary before deployment, but this Leopard update is worth installing.

 Size a Time Machine external backup disk to be at least 1.5x the size of all the hard drives that you'll be backing up. So, if you have an iMac with a 320GB hard drive, a 500GB Time Machine disk will give you all the protection your need. Be sure to include external hard drives in this calculation.

 An exception is if you know that most of the primary disk will be unused. In a business environment, many employees use only a small fraction of their hard drive space. If your users don't have movie files or a huge iTunes library on their work computer, they might only be using 40GB, 60GB, 80GB of disk space. Size a Time Machine volume accordingly. (For home machines, size based on the drive's physical size, not the amount of data used. Video and audio libraries grow and grow and grow.)

 If you have a choice of which interface to use for your external Time Machine backup disk, use FireWire unless you already have a FireWire external hard drive. If that's the case, use USB.

 If you have a choice of FireWire 400 and FireWire 800 on both your computer and external drive, use FireWire 800. You really want the fastest possible I/O bus.

 Although it's tempting to use the extra space in your Time Machine backup disk for "other stuff," resist the temptation, and consider the external hard drive to be dedicated to that purpose.

 From Systems Preferences, open Spotlight Preference and add the Time Machine external volume to the "Privacy" list. This tells Leopard not to index the Time Machine disk, which will improve both backup speed and general performance (and also save hard disk space).

 From the Time Machine Preferences page, make sure that the Time Machine volume itself is included in the "Do not back up" list. You can find this under the Options button.

 If you have anti-virus software installed, turn it off during the initial Time Machine backup. You'll find that this decreases the time of the initial backup by a factor of 4x or more. Be sure to turn the anti-virus software back on after it's done!

 To save disk space, consider excluding virtual machine disk images, such as from Parallels and VMWare, from your Time Machine backup. This will make backups more efficient. However, the virtual machines disk images won't be backed up either, so that's your call. However, if you just use a virtual machine to run Internet Explorer or Windows Media from time to time, note that the virtual machine image will change each time you use it -- and do you really want to backup and archive multiple copies of the disk image?

 If you use Aperture with Mac OS X 10.5.0 or 10.5.1, note that Apple recommends excluding your Aperture library from Time Machine. That's your directory called ~/Pictures/Aperture Library, where ~ is your home folder. Apple says that 10.5.2 resolves this issue.