There are many factors which combine to determine how long your backups will take. Some of them are obvious; some, perhaps less obvious.
1. The amount of data you're backing up.
Ask yourself if you really need to be backing up everything you're backing up. If disaster strikes, it may be better to perform a clean install from your OS X installation disc and then use Deja Vu to selectively restore items from your backup.
2. The amount of memory in your system. The speed of your system. The speed of your network if you're doing network backups. The type of device you're backing up to. The speed of your CD/DVD recorder if you're backing up to Toast.
Like most everything in OS X, Deja Vu will benefit from having more memory available to it. And, of course, backing up over a network will generally be much slower than backing up to a local FireWire disk, for example.
3. The level of system activity during the backup.
Deja Vu requires a fair amount of system resources while a backup is being performed. It also tries to be polite by running at a fairly low priority. If you are running other system-intensive apps during the backup, your backup may take longer. It's best to arrange to have your backups performed during periods when the system is relatively quiet (inactive).
4. The general health of the disks involved in the backup.
Make sure to regularly use a repair utility like DiskWarrior, Disk Utility, or AppleJack to fix any potential problems with your disks. Disk catalog corruption can cause any number of problems--from free space being misreported, to files not being displayed in the Finder.
5. The Deja Vu options you have selected. Each bit of functionality has a cost. Here are the options that will affect your backup speed.
- 'Repair disk permissions': This usually doesn't take too much time, and it can help keep your system in good health. Still, if speed is your primary concern, keep this unchecked.
- 'Show backup progress': The more data you are backing up, the more this option will lengthen the duration of your backup. The reason for this is that in order to show a "percentage complete", Deja Vu must first perform a "simulation scan" to determine the total number of files which will actually be copied. With more data, this simulation scan takes more time.
- Safety Net (available in DV 3.1 and higher): Safety Net provides a valuable feature in that it can archive changed and/or deleted files so that you can retrieve previous revisions of a given file. The amount of time this will take depends on the amount of data Safety Net needs to archive, and on the number of archives you ask it to keep for you (because an index of these archives is created each time a backup is performed).
Having either of these last two options enabled will cause DV to perform a simulation scan as described above. This means that if you have Safety Net enabled, you may as well enable 'Show backup progress' as well, since the cost is basically nothing in this scenario.
6. Spotlight (Tiger).
As of version 3.2, Deja Vu will temporarily disable Spotlight indexing on the destination disk (assuming it's enabled) for the duration of the backup. This is done to prevent Spotlight from frantically trying to index all the files that are being copied over.