I have CrashPlan backing up almost every file on my Hackintosh, and when CrashPlan runs, it caches a ton of data so it can run faster. However, they don't let you configure where that data is stored. In my case, I'm backing up around 1TB of data, and thus the cache is a whopping 8GB. 8GB might not seem like that much these days, but when it's sitting on your small SSD, it's quite annoying. Fixing this problem was pretty easy, and since plenty of people were complaining about this on their forums in different threads, I thought I'd post my simple solution here.
sudo launchctl unload /Library/LaunchDaemons/com.crashplan.engine.plist
rm -r /Library/Caches/CrashPlan
ln -s /Volumes/OtherDrive/path/to/new/cache/ /Library/Caches/CrashPlan
sudo launchctl load /Library/LaunchDaemons/com.crashplan.engine.plist
6. Restart CrashPlan