Error: "This backup is too large for the backup volume."

Question

Well TM is acting up. I get an error that reads:
"This backup is too large for the backup volume."
Both the internal boot disk and the external baclup drive are 1TB. The internal one has a two partitions, the OSX one that is 900GBs and a 32GB NTFS one for Boot Camp.
The external drive is a single OSX Extended part. that is 932GBs.
Both the Time Machine disk, and the Boot Camp disk are excluded from the backup along with a "Crap" folder for temporary large files as well as the EyeTV temp folder.
Time Machine says it needs 938GBs to backup only the OSX disk, which has 806GBs in use with the rest free. WTFFF? The TM pane says that "only" 782GBs are going to be backed up. Where did the 938GBs figure come from?
This happened after moving a large folder (128GB in total) from the root of the OSX disk over to my Home Folder.
I have reformated the Time Machine drive and have no backups at all of my data and it refuses to backup!!
Why would it need 938GBs of space to backup if the disk has "only" 806 GBs in use??? Is there anyway to reset Time Machine completely???
Some screenshots:
http://www.xcapepr.com/images/tm2.png
http://www.xcapepr.com/images/tm1.png
http://www.xcapepr.com/images/tm4.png

Answer 1

xcapepr wrote:
Time Machine says it needs 938GBs to backup only the OSX disk, which has 806GBs in use with the rest free. WTFFF? The TM pane says that "only" 782GBs are going to be backed up. Where did the 938GBs figure come from?
Why would it need 938GBs of space to backup if the disk has "only" 806 GBs in use??? Is there anyway to reset Time Machine completely???
TM makes an initial "estimate" of how much space it needs, "including padding", that is often quite high. Why that is, and Just exactly what it means by "padding" are rather mysterious. But it does also need work space on any drive, including your TM drive.
But beyond that, your TM disk really is too small for what you're backing-up. The general "rule of thumb" is it should be 2-3 times the size of what it's backing-up, but it really depends on how you use your Mac. If you frequently update lots of large files, even 3 times may not be enough. If you're a light user, you might get by with 1.5 times. But that's about the lower limit.
Note that although it does skip a few system caches, work files, etc., by default it backs up everything else, and does not do any compression.
All this is because TM is designed to manage it's backups and space for you. Once it's initial, full backup is done, it will by default then back-up any changes hourly. It only keeps those hourly backups for 24 hours, but converts the first of the day to a "daily" backup, which it keeps for a month. After a month, it converts one per week into a "weekly" backup that it will keep for as long as it has room
What you're up against is, room for those 30 dailies and up to 24 hourlies.
You might be able to get it to work, sort of, temporarily, by excluding something large, like your home folder, until that first full backup completes, then remove the exclusion for the next run. But pretty soon, it will begin to fail again, and you'll have to delete backups manually (from the TM interface, not via the Finder).
Longer term, you need a bigger disk; or exclude some large items (back-them up to a portable external or even DVD/RWs first); or a different strategy.
You might want to investigate CarbonCopyCloner, SuperDuper!, and other apps that can be used to make bootable "clones". Their advantage, beyond needing less room, is when your HD fails, you can immediately boot and run from the clone, rather than waiting to restore from TM to your repaired or replaced HD.
Their disadvantages are, you don't have the previous versions of changed or deleted files, and because of the way they work, their "incremental" backups of changed items take much longer and far more CPU.
Many of us use both a "clone" (I use CCC) and TM. On my small (roughly 30 gb) system, the difference is dramatic: I rarely notice TM's hourly backups -- they usually run under 30 seconds; CCC takes at least 15 minutes and most of my CPU.