Data requires more space on SSD vs regular HD?

Discussion in 'Mac mini' started by llcmac, Jun 17, 2012.

  1. llcmac macrumors newbie

    Joined:
    Aug 21, 2011
    #1
    Hi guys,
    I guess this is a general question on SSDs.
    I just installed a 256 GB Crucial M4 in my 2010 mac mini. I transferred the old data onto the new drive and there was a big discrepancy (almost 11 GB) in the used space between the two drives.

    I then reformatted the old HD and cloned the new SSD on it. Same 11GB difference in used space. Am I doing something wrong or is this normal for SSD drives?
     
  2. Poki macrumors 6502a

    Poki

    Joined:
    Mar 21, 2012
    #2
    It's either formatting difference or your SSD controller keeps some space for compressing data and speeding up your SSD.
     
  3. llcmac thread starter macrumors newbie

    Joined:
    Aug 21, 2011
    #3
    Well, both drives' formatting is "Mac OS Extended (Journaled)". As far as the SSD controller, is there a way to check or change its settings?
     
  4. Poki macrumors 6502a

    Poki

    Joined:
    Mar 21, 2012
    #4
    No, unfortunately you can't see or influence what the SSD controller does. Every controller handles compression, garbage collection and other features differently, so it's impossible to say what exactly your controller does (well, you could probably google it, but you probably won't find exact numbers).
     
  5. Ifti macrumors 68000

    Joined:
    Dec 14, 2010
    Location:
    UK
    #5
    Remember that the HDD also uses extra space on the physical disc when formatting for the MBR etc - its just that you cant see how much space its used.
     
  6. Puevlo macrumors 6502a

    Joined:
    Oct 21, 2011
    #6
    Pretty stupid if compression makes it take up more room.
     
  7. Pheo macrumors regular

    Joined:
    Jun 13, 2011
    #7
    Its not the compression, its potentially the wear levelling algorithm. In order to ensure the drive does not become saturated (leaving the controller with few options for swapping out dead NAND chips, etc), a reserve is managed by the controller.

    However the scenario you talk about could be any number of things, but without more info its not easy to tell.

    PS I'm doing a TX from a 120GB Intel SSD to a 256GB Samsung one tonight so if I notice anything odd I'll be sure to post back!
     
  8. llcmac thread starter macrumors newbie

    Joined:
    Aug 21, 2011
    #8
    The problem (?) is getting worse by the day. Now, the difference is over 15GB between my SSD and my nightly clone. At this rate I will run out of space within a few weeks. :) And I still have no idea what's causing this or if this is normal.

    Does anyone here clone their SSD drives for backup on regular spinning HDs and can confirm they are seeing the same thing?
     
  9. gnasher729 macrumors P6

    gnasher729

    Joined:
    Nov 25, 2005
    #9
    I think I know what's happening ("nightly clone" was the hint):

    Apple assumes that you are using Time Machine. So you don't clone your hard drive (make an identical copy), but use Time Machine to backup whatever is changed. That has the advantage that if you delete a file by mistake and find out next month, you can go to your Time Machine backup, go back a month, and get the file back.

    If you don't make regular Time Machine backups, Time Machine will make these backups on your computer's drive - as long as there is space. Of course the used space goes down, but if your drive gets full, Time Machine backups will be removed automatically.

    You could either use Time Machine for backups instead of cloning your hard drive, in which case the space used for Time Machine on your hard drive is recovered. Or you turn Time Machine off.
     

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