3 Replies Latest reply: Jul 24, 2012 5:50 PM by Linc Davis
dj_rag Level 1 (0 points)

hi all,


I havent used time machine to back up for a long time and during that period I changed laptop, came back to this one, and also replaced(upgraded) the hard drive.

My computer is about 494 GB full, and the external had drive i'm trying to use has capacity of 500GB. However, it wont do the backup because its saying "this backup is too large for the backup disk. The backup requires 588.66 GB but only 497.40 GB are available"


Does time machine really need almost 100GB of space to operate? Im away for the foreseeable future and do have a 1000TB ext. hard drive at home so i dont really want to have to buy another.


It says if I open time machine preferences I can make the backup smaller by excluding files however I dont imagine theres anything substantial I can delete that I wouldnt want a back up of.


Any advice welcome,

thanks in advance

macbook pro, Mac OS X (10.5)
  • Allan Eckert Level 8 (49,765 points)

    You have a much more serious problem then Time Machine. Seeing as how you only have 6 GB or less of free space you really need to start doing some serious housecleaning on your disk drive. Your free space should be ten time more then what you currectly have. If you don't do this you are standing a serious chance of corrupting your disk.


    You had better start either deleting or moving files ASAP.



  • dj_rag Level 1 (0 points)

    thanks for the heads up Allan, id heard that we should always keep some space but only ever read that 10 - 15GBs free was sufficient.

    Saying that, this MBP used to only have a capacity of 150GB and was always full to the brim, i was forever having to move things between external drives, its lasted me 5 years so far like that so I'm not too worried, but appreciate the advice cheers

  • Linc Davis Level 10 (184,915 points)

    According to Apple documentation, you need at least 9 GB of free space on the startup volume for proper operation. However, that wasn't the question. Time Machine pads out the amount of space required for a snapshot. The algorithm it uses to calculate the amount of padding isn't publicly known, but in practice, you need a backup volume that's at least two or three times the size of all the data you plan to back up to it.