Strange issue with Fusion Drive - how to tell if it's working?!

Discussion in 'iMac' started by eroxx, Aug 14, 2014.

  1. eroxx macrumors 6502a

    Jul 27, 2010
    Hi ..

    (deep breath)

    I have a mid-2012 27" iMac with 3TB fusion drive.

    The REGULAR SDD failed, and apple replaced it.

    However, my computer feels slower than it used to, and I'm thinking that the "fusion" magic isn't happening.

    Is there any way to tell definitively if the fusion drive is working?

    I am getting low numbers on blackdisk speed test, but my 3tb drive is also 90% full ... so I want to know if there's a simple definite way to check if it's working? Thanks!!
  2. dextr3k macrumors 6502

    Nov 26, 2012

    I do not have Fusion. However, if you open up disk utility, do you see 1 Mac HD, or do you see separate drives?
    If it feels slow, and you have doubts, maybe you could opt to try to reformat and install as new.

    however this is what its supposed to look like if it was working:
  3. drambuie macrumors 6502a

    Feb 16, 2010
    Go into System Info and look at the SATA data. If you select the HDD you should see the following bold headings in the data pane.

    EFI: which is disk1s1 and contains EFI
    disk1s2: which contains corestorage
    Recovery HD:

    The SSD should show the following:

    EFI: disk0s1 which contains EFI
    disk0s2: corestorage
    Boot OS X: disk0s3 which contains Apple_Boot

    As you can see, if Fusion is set up properly, the SSD is the boot disk. It's good to see that Apple assigned the recovery disk to the HDD.

    The two drives are linked logically, so the Disk Utility shows them as a single unit.

    You say the HDD is 90% full. Your SSD could also be nearly full, which could slow down its operation if there's a lot of swapping between it and the HDD. I don't know if there are any utilities that could show the usage date for each individual disk. DaisyDisk has two versions, and the non Appstore version has more capabilities that Apple didn't allow in the Appstore version.

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