Time Machine asking for more space

TimeMachine makes a complete backup the first time you use it and from then on it backs up just the files that have changed. Remember, the backups include your files, programs and operating system so when you upgrade an application or update the operating system that backup will be quite large. These incremental backups are done every hour (that the drive is plugged in). For this reason we veterans recommend that your drive be between 2-4 times larger than the data you are backing up. So if your drive has 100GB of stuff, your backup drive should be at least 200GB and preferably closer to 400GB. The bigger the TM drive the longer you can go without TM needing to delete old backups.

When TM doesn't have room to back up it will attempt to erase enough old backups so the new backup will fit. But if deleting all the incremental backups doesn't create enough space, TM is stuck. It sounds like that's where you are.

One other point -- since you're using one disk with two partitions (one for your real files and one for Time Machine to use), if the drive fails and goes bad, you will possibly loose both sets of files. Usually you want a separate disk to create backups on, so that only if both drives fail are you in deep trouble.

Drives are so inexpensive any more, that you really should consider this option. This will also let you sleep more securely and have one less thing to worry about ;-)

Good luck...