What if my Fusion Drive breaks?

Discussion in 'iMac' started by Notechy, May 20, 2015.

  1. Notechy macrumors member

    Apr 11, 2015
    The price reduction (£150 in UK) on the previously base retina iMac is bringing me nearer to a decision. But I am still on the fence re SSD v Fusion Drive. On balance, I probably prefer the convenience of a larger FD to the speed advantage of the SSD. But I hesitate over the cost consequences of the more probable failure of a FD beyond the 3 year point.

    So the question. If a FD fails, can the iMac work solely on the basis of external storage? Forgive my ignorance please.
  2. rkaufmann87 macrumors 68000


    Dec 17, 2009
    Folsom, CA
    Always backup and purchase AppleCare, these are your first lines of defense. If a FD fails it has to be replaced. It's that simple.
  3. fathergll macrumors 65816

    Sep 3, 2014
    Is this 100% accurate?

    I was told on here that you can technically decouple the drives if a failure occurs on one drive. I understand that your entire OS is toast if one drive fails but is it possible to decouple the drive in a failure and reinstall the OS on the working drive?
  4. sjinsjca macrumors 68020


    Oct 30, 2008
    Drives will fail. It's a "when" not an "if".

    It's also a bit of a myth that SSDs are more reliable than spinning disks. In portables, yes, this is true due to the elimination of moving parts. But for desktop use the difference is much smaller. And a failing hard disk might give warning... a failing SSD is more likely to die utterly.

    So either way, you need a solid backup strategy, ideally alternating between two backup disks, with an off-site component too. Time Machine makes the local backups easy, and restores too when (again, not if!) you need to do a repair. For the off-site component, I have had great luck with www.crashplan.com.

    As to separating the elements of the Fusion drive in the event of a failure, that strikes me as technically feasible but not easy and frankly not the greatest idea. Once a storage subsystem has failed, I would not trust any part of it. The flash component of Fusion drives works pretty hard in any case.
  5. xmichaelp macrumors 68000


    Jul 10, 2012
    Personally I would go SSD as I've had 2 HDDs fail and I would just prefer my sealed machine not have one in it. The less moving parts the better.

    If your fusion drive failed then you would still have the 128 GB of SSD in the machine a a boot drive. You could then just use externals for files.
  6. Fishrrman, May 21, 2015
    Last edited by a moderator: May 22, 2015

    Fishrrman macrumors Pentium


    Feb 20, 2009
    Yes, it can.
    You can use either the thunderbolt port, or a USB3 port, to boot and run a Mac from an external drive (HDD or SSD).
    Doing so with an external SSD will give very good boot and run times, although not quite the equal that you would get booting and running internally.

    But some other thoughts here, as well.

    Pardon my ignorance, but do the retina iMacs still use a SATA-based SSD, or are they using the new PCIe blade-drive technology?

    The PCIe blade drive SSD should be considerably faster than a SATA-based SSD.

    If you get an iMac with a fusion drive, you can actually run it two different ways:
    1. as a "fusion" drive, with the internal 128gb SSD and 1tb HDD "melded together" (the factory configuration),
    2. as a separate 128gb boot drive, AND a 1tb HDD (by "un-fusing" the drives manually, and having two drive icons on your desktop instead of the fused one).

    By un-fusing the drive, you will get the advantages of the SSD running at its full speed, all the time. The "disadvantage" is that you will have to manage the two drives as two separate volumes. Some folks have a problem with this. I have NO problems with it at all. I normally keep no less than SEVEN drive icons (volumes) on my desktop at all times.

    One other definite advantage of Un-fusing the drives is, if one of the internal drives fails, you will still have the other one operable with all the data that is still on it.

    If the fusion drive fails, you "lose everything" and will have to go to your backup.
    Aside: if one drive of the fusion drive fails, you probably can use Disk Utility and Terminal to get access to the remaining "good" drive, and "revive" it, but you'll still lose the data that was on the fused setup before the failure (again, this is why you need to keep the fusion drive backed up).
  7. Notechy, May 21, 2015
    Last edited by a moderator: May 22, 2015

    Notechy thread starter macrumors member

    Apr 11, 2015
    thank you for succinct clear answer. This is what I suspected. I trust that anyone having good reason to believe that it is wrong will explain how/why.

    I am not immediately tempted by your interesting alternative approaches. If I wanted to work with separate drives, I would be inclined to go for the internal SSD and an external drive, perhaps even a second SSD.
  8. hfg macrumors 68040


    Dec 1, 2006
    Cedar Rapids, IA. USA
    Here is how to split the Fusion drive into separate drives. Be advised that this will destroy any data on both drives, so be sure you have a backup to restore from before doing this.

    How to destroy a Fusion drive:

    The required Terminal commands are:
    (note: you can use diskutil list and diskutil cs list to obtain the volume ID's on your computer)
    diskutil cs deleteVolume < insert fusion logical volume ID here >
    diskutil cs delete < insert coreStorage logical volume group ID here >

    Look on page 2 of this article:

  9. vkd macrumors 6502a


    Sep 10, 2012
    You're right. If one of the drives fails, most likely the HD, the other will still be functional, although all data from the Fusion drive will be lost forever. You will be able to boot from another source, reconfigure the Master boot drive and install a fresh copy of Mac OS.

Share This Page