Run fusion drive with USB3 SSD

Discussion in 'iMac' started by mdb90, Jan 22, 2013.

  1. mdb90 macrumors newbie

    Dec 27, 2012
    Hi all,

    I've been looking around for a while and didn't find the answer I was looking for.

    Is it possible to create a Fusion Drive with this configuration:
    - iMac 27" late 2012 with 1TB (7200RPM) hard disk
    - an external SSD connected with USB3 (Silver River 5G, Corsair F240GBGS) should be very fast according to this thread:

    There are loads of sites out there which describe the whole process of creating such Fusion drive, however none of them seems to mention this option.

    Anyone done or tried this?

  2. Knuckleheadz macrumors member


    Sep 3, 2007
    United Kingodm
    yes but USB3 performance with an SSD is not great (about 200mb/s Read/Write) and USB also uses approx 10% CPU power to use it.

    Additionally you'll need to do it manually using Terminal and the CoreStorage command.

    There are also restrictions with a FusionDrive:

    • In its 3TB format you can't create a BootCamp partition
    • You can only create ONE partition on a FusionDrive - the option is greyed out in Disk Utility after you have made one (this can be a Mac or Windows partition)

    The preferred method for a FusionDrive using an external drive is a Seagate GoFlex External Thunderbolt Chasis and an SSD - you get approx 300MB/s, TRIM support and no CPU overhead.

    I've just ordered my 27" iMac without a FusionDrive, I plan to use a 240GB SSD connected with a Thunderbolt GoFlex unit for my boot partition and a second partition for my Audio Projects, then partition the 1TB up in to Samples, Data and a Windows Partition.

    Gives me the speed of boot and file transfer for my audio files and the control of multiple partitions - I am organised enough to move old Projects etc to the 1TB as I "archive them"

  3. Bear macrumors G3

    Jul 23, 2002
    Sol III - Terra
    Another issue is if your external drive loses power or gets disconnected while the system is running you will have to do some recovery work. How much recovery work depends on what the system is doing at the time. It could be anywhere from a few minutes to a lot longer.
  4. mdb90 thread starter macrumors newbie

    Dec 27, 2012
    Ah Bear, you've got a point there... :rolleyes: Maybe I'll stick with the easy way and just use it as a separate partition.

    @Knuckleheadz Hmmm, this thread: mentioned speeds up to 427 MBps read / 321 MBps write with that USB3 enclosure. Maybe that's just too good to be true. I'll see it tomorrow (hopefully). Will let you guys know my findings in case you're interested.

    I currently use a 2008 alu macBook, which also reach speeds of maximum 200 MB/s read/write, and that's already fast in my opinion.(due to Sata II interface) I might wait for some time and buy a thunderbolt enclosure as well when they're less expensive. (GoFlex will cost me around 200 euros for the enclosure only?)
  5. Knuckleheadz macrumors member


    Sep 3, 2007
    United Kingodm
    Just quoting something from that same thread...

    "find thread here start by user philipma (or quite similar name) - booting from usb 2/3 might end with system crash, as usb is dependant on CPU - under heavy CPUload system can simply crash - boot internaly, via FW or TB

    ..and I need my CPU cycles for audio processing too :)
  6. Tanax macrumors 6502a

    Jun 15, 2011
    Stockholm, Sweden
    Yes but based on the speed-test in the thread you've linked compared to various tests on the Seagate TB posted here on Macrumors, the USB3 case is actually faster.

    The only thing to consider is that USB3 can take up to 12% of CPU-power. If you're a CPU power-user(e.g. pushing your CPU), creating an overload for the CPU will cause the USB3-device to disconnect. And if you're booting from it, you computer will crash(as in a hard shutdown). This won't be an issue if you're not a CPU power-user but just something to keep in mind!
  7. tredstone macrumors regular

    Aug 25, 2010
    Has anyone been able to boot off a USB3 SSD with no reliability problems?
  8. Sindwal macrumors newbie

    Apr 23, 2013
    No, you can't. With the following configuration: 27-inch iMac, 3.2 Ghz, I5, late 2012, 16 GB RAM, SSD external LaCie Porsche Design P9223, NOT 'POSSIBLE TO CREATE A FUSION RUNNING DISK using the procedure found here: http:// /. The best possible result (after 22 attempts) is blocking the installation. It manages to have the folder on the disk fusion with elements of installation, but my next launch (which should use the data folder to finish the installation) does not give any result and the Mac restarts from the first traditional disk with the operating system.
    My conclusion is that Apple, on the latest set of computer market, has posted a firmware no documented that blocks the installation of a fusion disk if not installed by Apple itself. Conversely, the whole process is perfectly possible on all previous machines (marketed since at least 2009 onwards). Proof of this is that on my 24-inch iMac 2009, the process works perfectly on the first try. I suspect that Apple wanted to prevent the fusion drive solution was possible without using the services of Apple itself. A shame.

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