A clue may be lurking in your logs. See #A1 in [Time Machine - Troubleshooting|http://web.me.com/pondini/Time_Machine/Troubleshooting.html] (or use the link in *User Tips* at the top of this forum), for a handy widget that will display the backup messages from your logs. Use it to copy and post the messages here.
Is there anything besides your TM backups on that drive?
I couldn't get it to work again, so I deleted the sparsebundle on the backup drive. I then created a new sparsebundle, set it's size to 700gb, and copied it to the backup drive (networked). Then, I opened Time Machine's settings, selected the backup drive, and let it do a new full backup. It took over 10 hours, but it worked out fine. Now Time Machine is doing it's hourly backups again with no problem. My question wasn't answered, but I did get it working again. I still don't know why it was reporting the available space on the backup drive as 78gb when it was really 735gb? Must be a bug in Time Machine or something.
I'm seeing this on Mavericks (retina MBP, 500GB SSD about 60% utilized) . I've got a AFP network share that I copied a clean 800GB sparesebundle to. I use Disk Utility to mount and verify it, and it says, 650MB used, which means it's essentially 99% empty.
I unmount and attempt a backup with this disk. Almost immediately Time Machine reports that only 97GB free of the 800GB disk and can't continue because it needs ~275GB (a first time backup).
I unmount and remount it with Disk Utility and sure enough, it says it only has 97GB free. I re-run repair and the disk then reports 640MB used again. No matter what, Time Machine reports that only 98GB is free even immediately after I repair and even erase the Time Machine disk!
This is repeatable and reproducable.
The sparsebundle was created with:
hdiutil create -size 1000g -type SPARSEBUNDLE -nospotlight -volname "Backup of My Mac" -fs "Case-sensitive Journaled HFS+" -verbose [myhostname[.sparsebundle
rsync'd to the remote linux server that us running netatalk3 to share that volume.
I am mounting it as afp://mylinuxbox/TimeMachineBackup
This all works, disk utility recognizeses and validates the disk.
641MB used, ~840GB available.
I unmount the disk and the sparsebundle.
I attemped a backup:
I go to Disk utility, mount the disk and it reports:
I repair the disk, says its ok and the disk space returns to "normal". I can repeat this process endlessly to the same result. No matter what I try (erasing, new sparsebundle, etc) TM always says it's on;y ~90GB free.