Time Machine Back Up Question...

Discussion in 'Mac Basics and Help' started by Bazzy, Dec 18, 2010.

  1. Bazzy macrumors regular

    Jun 8, 2009
    Hi All,

    I have a June 2010 17" 2.66 i7 UMBP which has a 500GB internal HD. I recently purchased an external HD of the same capacity so I could keep a full back up of all my data.

    The internal HD shows capacity of 499.76GB with 160.24GB free. After connecting the external HD to the UMBP & doing a back up via Time Machine, it shows capacity of 499.76GB with 166.99GB free. This means there is a difference of 6.75GB between my internal HD & the back up one which to me seems a large amount.

    I can only assume that Time Machine has not backed up this missing 6.75GB of data & would like to know why this is so & what I can do to correct it. I have run Time Machine again a few times but the numbers still stay the same. Please can anyone else help me out here as at present, I just do not feel comfortable with they way things are & there is no way I can tell what data is missing on the back up HD - my luck is that it will probably be something(s) that might be important/critical in future!

    Many Thanks,
  2. simsaladimbamba

    Nov 28, 2010
    As you have a MBP you probably use the SLEEP feature (some don't, they just shut that thing down and start it up when needed, sometimes several times a day, which wastes a lot of energy),
    which, if you haven't changed any settings via Terminal or SmartSleep (www.jinx.de), usually saves the content of the RAM to the HDD in case of the battery running out (that's why the sleep light indicator can take up to 30 seconds to actually pulsate).
    Therefore you have a 4GB sleepimage file on your Mac.
    The other 2.75GB could have been used for swap files (when the RAM swaps data onto the HDD, to not lose the data and make room for more RAM or other parts of the system accessing RAM) and other temporary files Mac OS X does not need to back up.

    You can also take a look at OmniDiskSweeper or JDisk to scan both HDDs and look for the folders with different sizes.
  3. Bazzy thread starter macrumors regular

    Jun 8, 2009


    Many thanks for the reply - most grateful! I must admit that I am not too savvy at all on the technical side of things so I have great trouble understanding most things beyond basic level!

    As it was a first back up, it did take a vey long time & via system preferences (under energy savings) I selected the "Computer Sleep/Power Adapter" slider marker to "Never". I did this so it would not pause the Time Machine Back Up process as the computer would previously go to sleep if not used for 15 mins.

    Would this have been the cause for the missing 6.75GB of data in some way?

  4. simsaladimbamba

    Nov 28, 2010
    No. Have you ever put the MBP to sleep manually? If so, a 4GB* sleep image gets created. Look at Macintosh HD / Private / var / vm / and see for yourself.
    from http://forums.macrumors.com/showthread.php?t=265475

    Show / Hide hidden files in Mac OS X: http://www.macworld.com/article/51830/2006/07/showallfinder.html

    And you don't need to set the timer to "Never", as the MBP will not go to sleep during a TM backup process (hourly) and wait for the backing up to finish. If you don't do anything in between the hours you are away from the MBP and it is still running, there is really nothing to back up.

    * If you have 6GB RAM, a 6GB sleepimage gets created, and so on.
  5. Laurencia7 macrumors 6502

    Jun 3, 2009
    Hidden files take up lots of space, I had this same issue.
    Try this software, it's free and allows you to find your space hogs, and delete them, or etc. Just USE IT ON your internal, don't delete off your Time Machine. It will rotate over old files when it gets full.

    Disk Inventory X

    Otherwise, unless it doesn't backup at all, then you have little worry.

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