If you run out of space on a particular partition, but you have excess space on another partition you can relocate your data. Lets say you have 100 Megabytes left on /dev/hda1 but your have 10 gigs left on /dev/hda2. Lets say you have a folder on /dev/hda1 /home/user/backup that is over 2 gigs. Lets transfer these files to /dev/hda2 and then create a symbolic link at the original location so the folder can be accessed from the exact same location. For the example /dev/hda1 is mounted at /home/user/backup and /dev/hda2 is mounted on /home/user/backup2.
1) Create a new folder and move the contents.
cp -r /home/user/backup/* /home/user/backup2
Then check that the files have been successfully copied to the new directory. Then delete the original backup directory.
rm -r /home/user/backup
Then create a symbolic link to the backup directory.
ln -s /home/user/backup2 /home/user/backup
Now when you navigate to /home/user/backup you wont be able to tell the difference except that you have now alot of space on the /dev/hda1 partition.
Your partitions may be mounted to different locations, just apply the above example to your particular configuration.