Fusion Drive - Determining How Much Each is Filled

Discussion in 'Mac Basics and Help' started by p3ntyne, Feb 22, 2014.

  1. p3ntyne macrumors 6502

    p3ntyne

    Joined:
    Jan 10, 2014
    Location:
    Sydney, Australia
    #1
    Hi,

    I have just loaded lots of data onto my fusion drive and I am wondering if there is any way to know how full each drive is.

    Thank you.
     
  2. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #2
    Not really... the system sees the Fusion as one drive. In theory though, the flash portion would always be almost full as the system tries to move the most frequently used data to that device.

    Give this article a read. You can sort of deduce where data is stored by watching disk activity using iostat while you copy files around.
     
  3. Tumbleweed666 macrumors 68000

    Joined:
    Mar 20, 2009
    Location:
    Near London, UK.
    #3
    As per Weaselboy, the flash portion should always be full or nearly so, but what its full with will change, so there is no point knowing what with, and the only thing that will change is how full the hard disk part is as you gain or remove data.
     
  4. blevins321 macrumors 68030

    Joined:
    Dec 24, 2010
    Location:
    Winnipeg, MB
    #4
    I believe that you can do Applications>Utilities>Terminal.

    Try the following two commands:

    diskutil list

    diskutil CoreStorage list

    It will tell the actual used space for each partition. Can't remember if the first one will give the individual components for a fusion drive or not.
     
  5. gnasher729 macrumors P6

    gnasher729

    Joined:
    Nov 25, 2005
    #5
    The OS tries to have the SSD drive full except for 4 GB that are used as a write cache. When you write data the write cache is filled; when you stop writing the OS empties the write cache so that the SSD drive has 4 GB free again. If you delete data that happens to be on the SSD drive, then the OS fills it up again with data from the hard drive when you stop using the drive for a second.
     
  6. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #6
    That will show the total space used by the Fusion logical volume, but it does not break it down by the individual, physical disks. It will just show the size of each physical disk, but not space free/used.
     

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