Question about Fusion Drive

Discussion in 'iMac' started by lixe, Jan 15, 2013.

  1. macrumors member

    Jan 26, 2010
    I have a question about the method fusion drive works: If I copy for example 1TB of data, especially the first time migrating from my old Mac, to the fusion drive, is everything then copied first to the SSD and only direct to the HDD in case the SSD is full (what will happen very fast in this case) or is it copied right away to the HDD and then later on some files will be moved to the SSD?
    Because I think apple told when they were presenting the fusion drive, that everything will be copied to the SSD in the first place so everything will happen super fast. But in case of a big data amount I don't think that's useful and more importantly actually not even doable?
  2. macrumors 603


    Apr 13, 2010
    This is a flaw in fusion with a 128gb ssd and a 1tb hdd. if you had a 512gb ssd or a 256gb ssd the problem would be smaller.

    Apple's osx will decide the sorting of the info. Based on how you use it.

    I can tell you one thing right off the bat having a 1.128tb fusion drive with 1tb of info is not a good idea. If you have that much info to load you do not want a 1.128 fusion drive.

    I have a 2012 2.3 quad mac mini I built a diy fusion with a 512gb samsung ssd and the 1tb stock hdd. No worries.
  3. macrumors 6502a

    Jan 4, 2013
    It's an interesting question...I would like to know if they're both pretty much filled and you start to use a lot of files on the disk, how does it open up room on the SSD to start placing files there as it moves from one drive to another. I thought I read somewhere that 4gb is reserved on the SSD.
  4. thread starter macrumors member

    Jan 26, 2010
    I want to get a 3TB fusion drive and think I will need mainly about 1.5TB or 2TB at the moment, so that shouldn't be a problem hopefully!
    I was just curious about the way fusion drive handles a big amount of data. If I for example import photos from my CF card I think it's really helpful if they will be stored on the SSD first, but if the amount excesses 128GB it's interesting what exactelly will happen :)
  5. macrumors regular

    Sep 3, 2011
    This Ars Technica article explains it well. All writes go to the SSD, so it will first fill up the SSD, then spill over onto the spinning disk. When the copy is done, the system will move 4G of data from the SSD to the spinning disk.

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