Time Machine question: backed up 9 gbs, but I was on vacation!

Discussion in 'macOS' started by ero87, Jan 20, 2008.

  1. ero87 macrumors 65816

    ero87

    Joined:
    Jan 17, 2006
    Location:
    New York City
    #1
    Hey friends,

    Time Machine gives me an error message whenever the memory in my external hard drive gets very low, so i like to keep some extra space in my external hd. Anyway, I just came back from winter break to my iMac, fired it up, and Time Machine had 9 gb of stuff to back up. What?! Where could this have come from, my computer was off, no one touched it!

    I'm curious if I have some strange setting on that is causing this erratic behavior. Any advice would be much appreciated :)
     
  2. tibi08 macrumors 6502a

    tibi08

    Joined:
    Sep 17, 2007
    Location:
    Brighton, UK
  3. georgeoommen macrumors regular

    Joined:
    Apr 12, 2007
    #3
    This is a commonly misunderstood phenomenon with Time Machine.
    When Time Machine says "backing up [x]MB of [y]GB", it doesn;t really mean that it is copying that much info from your computers hard disk to the Time Machine disk. That size also includes the compacting of the time machine backups that it had done in the past.

    Time Machine backs up hourly for the the past 24 hours. After 24 hours, it deletes/merges (i'm not sure yet) 23 of those backups and stores just 1 backup for that day. After a month, it again deletes/merges more of the daily backups and creates weekly backups. So the amount of data shown actually includes the amount of data Time Machine has to move around when doing this deleting/merging. I have been testing this precise thing for the past week and this is my finding. I have left my MBP switched on and untouched for the past week and last night i noticed it wanted to backup 47GB of data. My external HDD had only 65GB free. But when it finished the backup, I still had about 64.8GB free. Meaning it just moved the data around and added just about 200MB to the existing backups.

    Regarding the deleting/merging confusion, though I haven't been able to come to a precise conclusion, from what i'm seeing, i think it does some kind of smart merging of data but i can't report on that just yet. Will post again once i have conclusive evidence of what goes on here.

    Hope this helps.
     
  4. cmaier macrumors G3

    Joined:
    Jul 25, 2007
    Location:
    California
    #4
    Or he could have left something like Entourage, Parallels, or Fusion running, without setting Time Machine to ignore the applicable files.
     
  5. SawTooth500 macrumors member

    Joined:
    Nov 9, 2007
    Location:
    Florence, Arizona
    #5
    If he had to fire it up after returning from break, there shouldn't have been anything running. The machine was off!
     
  6. ero87 thread starter macrumors 65816

    ero87

    Joined:
    Jan 17, 2006
    Location:
    New York City
    #6
    welll now Time Machine just won't run, it gives me a very non-descript error message. I guess I'll just turn it off - this application still is buggy.
     

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