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Time Machine:The backup disk ran out of space unexpectedly. .....

22765 Views 28 Replies Latest reply: Mar 19, 2014 9:37 AM by vanclute RSS
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Gloria M Level 1 Level 1 (0 points)
Currently Being Moderated
Aug 2, 2012 6:23 PM



I upgraded to Mountain Lion when it was released and yesterday I began getting this notice from Time Machine:


"The backup disk ran out of space unexpectedly. Time Machine will try to make more space available by removing expired backups during the next scheduled backup."


I have a one terra external hard drive with exclusively Time Machine.  It says it has 3.4 gigabytes available, but isn't deleting old backups and making room for new, like before.  I tried the "encrypting" solution, but it still keeps on giving me this message.  Should I erase and format?  If so, what option should I chose to format?


My Hard Drive has 240 gigabytes, so 1Tb should be more than enough.


Thank you!



  • Kappy Level 10 Level 10 (221,095 points)

    About TM "Backup Drive is Full"


    Alert TM only deletes older files if they have been deleted from the source and when TM needs space on the backup drive for a new incremental backup. Time Machine "thins" it's backups; hourly backups over 24 hours old, except the first of the day; those "daily" backups over 30 days old, except the first of the week. The weeklies are kept as long as there's room.


    So, how long a backup file remains depends on how long it was on your Mac before being deleted, assuming you do at least one backup per day. If it was there for at least 24 hours, it will be kept for at least a month. If it was there for at least a week, it will be kept as long as there's room.


    Note, that on a Time Capsule the sparsebundle grows in size as needed, but doesn't shrink. Thus, from the user's view of the TC it appears that no space has been freed, although there may be space in the sparsebundle.


    Once TM has found it cannot free up enough space for a new backup it reports the disk is full. You can either erase the backup drive and start your backups anew or replace the drive with a larger drive.

  • Kappy Level 10 Level 10 (221,095 points)

    SuperDuper and Time Machine are two completely different backup utilities. If you want something like what SuperDuper does then don't use Time Machine. You have many other options that won't use up all the space on your backup drive:


    Backup Software Recommendations


    Carbon Copy Cloner

    Data Backup

    Deja Vu


    Synk Pro



    Others may be found at VersionTracker or MacUpdate.


    Visit The XLab FAQs and read the FAQ on backup and restore.  Also read How to Back Up and Restore Your Files.


    Do the following to erase your drive:


    Erase a Drive


    1. Open Disk Utility in your Utilities folder.


    2. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.


    3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed.

  • Pondini Level 8 Level 8 (38,710 points)

    If you just want to erase the drive, see #2 in Using Disk Utility.

  • Pondini Level 8 Level 8 (38,710 points)



    Glad it's sorted out, and thanks for the feedback.

  • pugdogfan Level 1 Level 1 (0 points)

    I have the same problem but would like to know if there is a less risky way to purge selected backups rather than leaving myself with no backup whilst a new one is built.


    I would suggest that in such circumstances, an automatic consolidation of the incremental backups  is a better solution than "buy a bigger disk" or "erase your backups" and hope nothing goes wrong whilst you exercise every part of your drive whilst the backup is re-created.


    Or even a manual consolidation would be better than those hours between erasure and the backup completing. Adding a "Consolidate backups" to the menu which pops up in Time Machine would be an easy compromise to implement.

  • Pondini Level 8 Level 8 (38,710 points)

    pugdogfan wrote:


    I have the same problem but would like to know if there is a less risky way to purge selected backups rather than leaving myself with no backup whilst a new one is built.

    Normally, Time Machine will delete your oldest backup(s) to make room for a new one.


    If it runs out of space unexpectedly, it means there was a problem with the estimated size of the backup (much too small), or something happened causing a much larger backup than expected.


    If that's the message you got, try this:


    Verify your internal HD and repair your backups, per #A5 in Time Machine - Troubleshooting, then Restart your Mac, to be sure there isn't a directory problem causing this.


    If that doesn't help, try deleting the partial backup, per #A10 in the same link.


    If you got a different message, see #C4 in the same link.

  • pugdogfan Level 1 Level 1 (0 points)

    Genius Pondini - it was an internal disk problem, fixed by following your instructions, including running repair twice after the first pass didn't fix everything.


    Backup sorted itself out without further problem.


    Many thanks for your help.

  • ryantoyota Level 1 Level 1 (0 points)

    I just wanted to leave a note that Kappy's response was NOT THE CORRECT ANSWER for the problem mentioned. Yes it "solved" the problem but at the expense of losing any past backups, which is not needed.


    I had the same issue on two of my computers (one that had 320GB of free space on the backup drive) and when I kept getting this message I started watching the Time Machine progress when it tried to back up. It would estimate an amount of space needed for backup, start to back it up, and then when it got close to the end the size needed would start increasing the required backup size until it filled the available space on the drive. The key word in the error message shown is UNEXPECTEDLY. This is an error message, not a standard "Backup Drive Is Full" notification message.


    Pondi's post below nails the problem and provides a solution that worked for both of my computers. It might be worth noting that this problem started occuring on my work computer after I turned on iCloud syncing, suggesting it may be one of the files that was synced with iCloud that is causing the calculation error. Whatever the initial cause, Pondini's suggestion of verifying the internal hard drives and repairing the backup drives worked for me (and with pugdogfan as well it seems).


    Hopefully this post helps prevent anyone else with this issue from needlessly reformatting their backup drives.

  • John Christopher1 Level 1 Level 1 (15 points)

    Thanks Pondi and Ryantoyota. I've had this happen twice now. !st time I reformatted my hard drive. This time I know better.

  • prague Level 1 Level 1 (0 points)

    My problem seems similar. I use a mac pro with a 2 TB g drive as a time machine and also other stored files. The drive now shows, both with disk utility and by measuring all files with info, that I have only about 380 GB free space. If I measure the size of all files, including the backups, I have only stored about 900 GB and should have about 1100 GB free. A repair of the disk shows no problems.

    Why doesn't the machine see the actual free space. Has the time machine program reserved space for backups or is there another problem? How can I free up the real free space on the drive?

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