After recently installing Leopard (MacOS X 10.5) I've had great success with Time Machine on my nearly-aways-connected external USB 2 drive. After recently modifying the preferences of some web-based applications (like FireFox or Second Life) I came to the realisation that Time Machine is also backing up all my caches.This is a problem for two reasons; one is technical, one other a matter of security and privacy.
- Time Machine only backs up changed files. On my machine, the only files that change on a regular basis (including additions) are my thesis documents and, you guessed it, my cache folders. Why should I expend processor resources and, more importantly, disk space to back up my cache files? In short, there is no good reason.
- If you empty your caches in an attempt to improve security or to ensure some level of privacy, Time Machine will, every hour, nullify that effort.
There is, thankfully, a very simple way to fix this. Just add whatever folders you don't need backed up to Time Machine's "Do not back up" (i.e., exclusions) list, by pressing Options in System Preference's Time Machine module, and adding them. To increase efficiency as well as backup drive space, I have also elected to exclude:
- Downloads folder. The ~/Downloads folder is meant as a spool space: you take something from there and then do something with it (copy it to your Documents folder, or install it and trash the .dmg, or what have you). It is wholly redundant, for me, to back up my Downloads folder.
- Movies folder. Similarly, I keep all relevant video media on an external drive; files in my Movies folder are simply copies of the masters that reside elsewhere, copied to my local disk because I want to watch them soon, or potentially offline. Backing up these is also redundant.
- Developer Tools folder. As I save the installation media (be they updates from ADC as .dmg files, or the Mac OS X installation DVD), backing up the developer applications is redundant and a waste of space. Of course, I do back up my programming projects, which reside in ~/Developer.
- /Library/Audio folder. This is where the GarageBand Jam Pack loops are stored. That alone eats about 25 % of my hard disk space, and since I always save the installation media, backing up the installed, uncompressed loops is an important waste of space.
I should add that, despite the–to some horrifying–lack of configurability in Time Machine, it does serve its purpose, even for a power-user like me. I would like to see more options, but when it comes down to it, I probably wouldn't use them. Yes, even changing the backup schedule. I think, for a twit like me, hourly is just fine. For comparison, I'm the type who sets his word processor's "Auto-save every: " to one minute, begrudging the lack of granularity in scheduling.
