APFS and Fusion drive, as two drives

Discussion in 'macOS High Sierra (10.13)' started by MortyUA, Oct 22, 2017.

  1. MortyUA macrumors newbie

    Jul 3, 2012
    Hi there,

    Sorry to ask a n00b'ish question, but I'm a mostly-Windows guy who just needs to check a single thing:

    If I have a Mac desktop (iMac) with a Fusion drive, then APFS isn't supported and the default is to keep the older HFS+

    But I assume I can install 10.13 and use APFS, I just have to install leave the two drives separate, and install the OS to the SSD, and have the magnetic HDD as a second drive.

    Am I right in my assumption? :O
  2. dianeoforegon macrumors 6502a


    Apr 26, 2011
    Yes, you are correct. There is one other option....wait until Apple supports APFS on fusion iMacs.

    I 'defused' my iMac and am happy with the results. Depending on the size of your SSD you might need to review the size of your email. Both Mail and Outlook 2016 store your data in the User's Library. I wouldn't advise trying to move your User's Library to the rotational drive.

    These are my notes on how to disable fusion drive. Needless to say you MUST backup first. This will destroy all data. I suggest a clone rather than Time Machine. It would be easier to restore files to the correct drive.

    Follow this article, especially page 2.

    Boot in recovery mode, then open terminal, and type these commands:

    diskutil cs list

    This command will show you the IDs you need to delete fusion drive.

    diskutil cs deleteVolume < insert fusion logical volume ID here >
    diskutil cs delete < insert coreStorage logical volume group ID here >

    These commands will split the drives apart. Once the drives are separated, you can rename those drives in Terminal, because you can't use Disk Utility: it will try to fix the Fusion Drive for you.

    diskutil list

    This command will show you the identifier for the two drives, that you'll use this way:

    diskutil rename disk0s2 Macintosh HD
    diskutil rename disk1s2 Data HD

    Exit terminal, click on "Install OS X" and select the SSD, and you're good to go. Once in disk utility in OSX, the drives will be listed normally.

    Software used to Clone:
    CarbonCopyCloner http://www.bombich.com/download.html (All options are available free for 30 days)
    SuperDuper! http://www.shirt-pocket.com/ (Free forever to do an erase and install. Purchased version allows for smart updates and schedules)
  3. MortyUA thread starter macrumors newbie

    Jul 3, 2012
  4. psymac macrumors 6502a

    Jul 17, 2002
    I'm planning to defuse a 27" iMac 2017 with 2TB HD, are your read/write speeds close to that of the 512k SSD?
  5. Macintosh1984 macrumors regular

    Dec 15, 2012
    Hi! Is it possible install HS on a Fusion Drive disabling APFS, so having the old HFS+ system? When installing HS, there is a chekbox to uncheck?

    Do yuo think that when APFS came out to Fusion Drive, we need to reformat again the Mac or HFS+ to APFS will be a normal upgrade without data lose?
  6. woodbine macrumors regular


    Aug 8, 2010
    Bath, UK
    Just now, software update is asking me to upgrade to 10.13.1, this is the first time I’ve had a prompt for HS. I have a fusion drive. Does this mean HS is ready to install on fusion drive without separating the SSD and HD?
  7. Macintosh1984 macrumors regular

    Dec 15, 2012
    Defusing "Fusion Drive", boost Mac? So I can install HS with the new file system?

    Defusing invalidates the warranty?

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6 October 22, 2017