How much bigger hd is needed for time machine?

Discussion in 'macOS' started by Wie Gehts, Sep 5, 2009.

  1. Wie Gehts macrumors 6502

    Mar 22, 2007
    I never used this before and added a partition to an ext with what I thought would be enough space....the hd I have SL on is approx 375gb, but only about 40gb of stuff is installed.

    So I made a partition on the ext for 250gb, but then time machine said I'd need 302gb. So I'm thinking...for what? 40gb worth of stuff??

    Then I realized time machine has to hold alot more stuff in relation to what the hd its time machining.

    My question is.....just how big, or how many times bigger, does the time machine hd ideally need to be above the hd its copying from? 2x, 3x, 10x 100x?

  2. NP3 macrumors regular

    Jul 12, 2003
    Los Angeles
    As a side note, I read awhile ago it is generally not a good idea to partition an external drive. I'm not sure if that is still true. My backup is only about 2x bigger. It comes down to how many old copies you want saved.

    My drive did get full, so it'll periodically delete the oldest redundant backups. And it tells me what that updated date is for the oldest complete hard drive backup. Right now its December 13th of last year. Hope this helps.
  3. iLog.Genius macrumors 601


    Feb 24, 2009
    Toronto, Ontario
    Depends on what you have saved on your computer. 250GB is really cutting it close but works for some people, I don't recommend it. 320GB is ok if you don't save a lot of media to your HDD. 500GB is probably used by most users and then 1TB is for the those who tend to save a lot to their HDD. Usually it comes down to what you have on your HDD, it would come down between 500GB and 1TB.
  4. spillproof macrumors 68020


    Jun 4, 2009
    I read a few time that your best bet for backup storage is one that has twice the storage as your internal drive. Same for TM partitions.
  5. TheMechanic macrumors regular

    Mar 2, 2007
    Can somebody explain why that is so?
  6. Chupa Chupa macrumors G5

    Chupa Chupa

    Jul 16, 2002

    It depends on how far back you want to archive your data. The bigger the TM drive is in proportion to the sum total of data you are archiving the more # of days you'll be able to go "back in time."

    Keep in mind that TM's beauty is that it is a dynamic archive since it's keeping track of changes ove a period of time. Because of that it needs extra headroom to store those changes. If all you want to do is back up what is on your computer right now, and only be able to retrieve that data -- not what you did last week or month, then you might want to look at SuperDuper or Carbon Copy Cloner for your back up needs.
  7. Wie Gehts thread starter macrumors 6502

    Mar 22, 2007
    thanks all

    yeah, i have superduper on the brain which is why it didn't at first occur to me that time machine needed more space than a clone 1:1 relationship.

    as far as not partitioning ext drives....well that just can't be right. not that i have proof at the moment, but not being able to do something so simple and functionally necessary...can't be true
  8. miles01110 macrumors Core


    Jul 24, 2006
    The Ivory Tower (I'm not coming down)
    I have a TM backup drive that's 1.25 the size of my internal hard drive. It hasn't run out of space in over 3 months, and if it did old backups would just be deleted to make room.

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