"Backup too large"...but i still have room on HD!

Question

So I have a 300 GB external HD, and this issue keeps on popping up. Its the 3rd time its happened now. Both previous times, I have just started over, reformatted external drive and started Time Machine from scratch again. I'm real tired of doing that.
So heres the problem: After a while of normal updates, (usually a few weeks or so) at some point I encounter a Time Machine error message stating: "This backup is too large for the backup volume. The backup requires 91.0 GB but only 60.1 GB are available." ( well obviously that last part changes. But thats specifically what it says right now).
OK, so isn't TM supposed to do incremental backups and then when it runs out of space, start deleting the oldest information? Thats my understanding. So in other words, maybe i start losing backups from a month ago or so, but I should still have recent backups. However, when I go into TM, it has not been backup up since I first got that message. The earliest I can go back to is July 20th in Time machine (even though I should be able to access July 21-Today,August 2). Although its true that i only have 60GB left on my external HD, why is TM trying to do a 91GB backup? I have not added 91GB of stuff lately.
My iMac HD is 297GB, so even if that was totally full, since my external is 298GB, i technically should NEVER get a message that my backup is too big. I guess worst scenario, is that my backup only goes back a day or two, when my Imac hard drive is maxed out.
Thanks in advance for any help!
Darren

Answer 1

DauthiSlayer wrote:
So heres the problem: After a while of normal updates, (usually a few weeks or so) at some point I encounter a Time Machine error message stating: "This backup is too large for the backup volume. The backup requires 91.0 GB but only 60.1 GB are available." ( well obviously that last part changes. But thats specifically what it says right now).
As Larry says, your TM drive is wayyyy too small.
But it looks like something else is going on here, too, that's causing extra-large incremental backups. Whatever that is, getting a larger disk will allow more room for those backups, but won't make them any smaller.
There are some OSX features and 3rd-party applications that cause large Time Machine backups. Common ones are FileVault, vmWare Fusion, Parallels Desktop, Entourage, and Thunderbird. Any application that uses a single large file or database may do this.
FileVault (System Preferences > Security) converts your entire Home Folder into a single, encrypted disk image. So any change to anything in your Home Folder is treated as a change to the encrypted image, and the whole thing is backed-up. TM minimizes the impact, though, by only backing it up when you log out, but it's still going to eat up a lot of space on your TM disk.
Some apps, such as Entourage, sometimes use a single file, often a database, to store their data. With Entourage, for example, every time you send or receive a single message, the whole database is changed, and will be backed-up the next time. Apple mail, of course, stores messages individually, so this doesn't happen.
We've also seen this with folks using the +Directory Backup+ feature in the +Tech Tool Pro+ app. It makes lots of large files in a: +*~/Library/Application Support/TechTool Protection/<name of hard drive/*+ folder.
If in doubt, Click here to download the TimeTracker app. It shows most of the files saved by TM for each backup (excluding some hidden/system files, etc.).
One solution is to simply exclude the item from TM so it isn't backed-up regularly, then when you do want it backed-up, just copy it somewhere that's not excluded.