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Time Capsule Backup smaller than Hard Disk size

1855 Views 11 Replies Latest reply: Jan 22, 2013 1:20 AM by Sergio727 RSS
Chau Calculating status...
Currently Being Moderated
Feb 16, 2012 3:50 AM



I just got a new Time Capsule, 4th gen to backup my Mac.  I have previously used a 1st gen Time Capsule without any issues and so I am wondering why my first back up with the new TC is smaller in size compared to my HD.  The TC backup is about 294 GB and my HD is 319 GB in size -- a 25 GB difference.  I read in other Apple Support Community discussions that a small discrepancy in size is not an issue, but I assume that 25 GB is a significant difference in size?  I have nothing excluded from the Time Machine backup preferences.


Thank you for your help.

MacBook Pro, Mac OS X (10.7.2), Aperture 3.2.1
  • LaPastenague Level 7 Level 7 (32,820 points)
    Currently Being Moderated
    Feb 16, 2012 6:37 PM (in response to Chau)

    Where are you getting HD usage from?? It is measured in different ways in different places.


    Also look at Virtual Memory used in your Mac. The amount might surprise you.



  • LaPastenague Level 7 Level 7 (32,820 points)
    Currently Being Moderated
    Feb 17, 2012 8:07 PM (in response to Chau)
    (1)  I renamed my TC base station with the same name from the previous attempt where I experienced errors.  Will this effect my new attempt at backing up with TC and TM?  Are there preferences and settings hidden that might make TM think it is backing up on the old TC base station?  Should I have used a different name or does this not make a difference?


    It won't make any difference.. TM will find no existing backup and will start again.




    (2)  TM seems to be backing up about 294GB once again and not the 308GB that I am expecting (the size of my HD after restarting the computer).  There is a 14GB difference, is this significant?  How can I find out what exactly is not being backed up onto TC by TM?


    Thanks a lot for your much needed help and input.

    I think you are still worrying about nothing.. if you want to do a backup which is more certain, do a disk image. You can do this with superduper, ccc, several other backup packages.. my favourite is clonezilla which uses a linux boot disk, but you might find it difficult to operate.


    TM is not a disk clone. It is a file backup.. as such there are temp files which are not backed up.. there are also different ways of measuring files.. due to inefficiency of storage on a hard disk, a large number of small files will take up 20-50% more space than the actual file size.. the hard disk size will reflect used sectors not file bytes.. when a file is backed up, TM breaks it into small segments.. which fully occupy the sectors on the hard disk.. this added efficiency allows the backup to be smaller than the files on the drive.. don't worry it will rapidly get bigger than the hard disk.


    Read how TM actually works.


    It is rather different to what you imagine.

  • michaelcharliehunter Level 1 Level 1 (5 points)
    Currently Being Moderated
    Dec 13, 2012 3:34 AM (in response to Chau)

    I know this was a while back Chau, but thought I'd throw my 2 cents in (I also came across this while changing over TC's).


    I had a ~600GB "backup" of my entire drive that only took about 230GB out of my TC - a HUGE discrepancy. I even manually backed up a few times to see if there was data that hadn't gone through the first time. If you go through and check all your 'document' folders though; Desktop, Movies, Photos etc .. their sizes should still equal what TC actually backed up. That's because your Mac has all those applications (as well as everything LaPastenague mentioned) that don't get backed up. I have Logic Pro for example (approx 200GB), and a few other space hungry apps which Time Machine doesn't backup locally to my TC. It's just the personal files and settings etc.


    Just in case you were still wondering, hopefully that clears it up

  • Sergio727 Level 1 Level 1 (0 points)

    Michael, I have a similar situation to Chau, hence why I landed here. "Mac Basics: Time Machine" ( says that applications are indeed backed up -- "Time Machine automatically backs up your entire Mac, including system files, applications, accounts, preferences, email messages, music, photos, movies, and documents." I have a 60GB discrepancy on mine, which is worrying. Drilling in I found that the Cache for Album Artwork in iTunes folder was not backed up - and that's OK, but that's only a couple hundred MBs. I still haven't figured it out. Why do you think that your Time Machine singles out Logic Pro not to be backed up? Thanks!

  • michaelcharliehunter Level 1 Level 1 (5 points)
    Currently Being Moderated
    Jan 21, 2013 7:58 PM (in response to Sergio727)

    Yeah I've since found out that all is indeed backed up Sergio (going into Migration Assistant shows the various things you can restore from backup).. I just assumed it was only personal files, but since that's not the case, I wouldn't have a clue..


    I haven't had an issue with things missing from backup (so far).. So I guess it's the case of not fixing something if it isn't technically broke. Might mention it to a genius the next time I'm at a store ;)

  • Sergio727 Level 1 Level 1 (0 points)
    Currently Being Moderated
    Jan 22, 2013 1:20 AM (in response to Chau)

    Hi Michael, Hi Chau, thanks for your replies and the link. Actually, I think I might have found the discrepancy. I checked each "high level" folder (Downloads, Documents, etc), some of which showed minor variations but no 60GB. Finally, with invisible files unhidden, I found "MobileBackups", with a size of ~60GB. Indeed, there's a lot more info on this on the website LaPastenague had point to, specifically - Again, thanks all for your help on this!


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