4k 21.5" iMac. Fusion Drive vs HDD + external SSD?

Discussion in 'iMac' started by gabrielsanz, Jan 31, 2016.

  1. gabrielsanz macrumors newbie


    Jan 31, 2016
    Hello all,

    This is my first time in this forum and I am sure this question has been asked a lot but I cannot find an answer to my specific question.

    I am about to purchase a 21.5" 4k iMac and would like to know if getting the base model with the 5400rpm HDD and booting from a thunderbolt external SSD would be the same as getting the 1TB fusion drive with just 24GB of SSD.

    Can I save money and get a larger SSD for the same price or will this setup be slower than one with a fusion drive?

    Thanks in advance!
  2. ljonesj macrumors 6502a


    Oct 20, 2009
    Kingsport TN
    the thunder bolt boot up would be faster than the 5400rpm drive you can also for cheaper get a usb 3.0 enclosure that suppors usap which is a scsi interface that takes the load off the cpu and lets u use usb 3.0 as the boot ive done that with my imac late 2015 27in 5k with the 1tb fusion and its on par and my 1tb fusion gets close to 800mbs read
  3. Sirmausalot macrumors 6502a


    Sep 1, 2007
    although it will work, in the long run you'll be mch happier just getting the right thing from the start. for budget, get a 2tb fusion and be done.
  4. gabrielsanz thread starter macrumors newbie


    Jan 31, 2016
    thanks! how would a usb 3.0 and a thunder bolt ssd compare? Is there a big difference in performance?
    I'm working with a budget and really need the computer soon. Ordering the custom computer from the apple website where I live (2tb FD+shipping+sales tax) is substantially more expensive than just going to the nearest Best Buy and getting a base model I can work with. No apple stores here :/
  5. Flow91, Feb 1, 2016
    Last edited: Feb 1, 2016

    Flow91 macrumors newbie

    Dec 10, 2015
    Hi, the problem is that the USB port limits the transfer speed of the SSD. It seems like e.g. a Samsung Evo 850 gets about 350 MB/s write and read, while the intern iMac SSD can reach 900 MB/s. Thunderbolt should be faster than the USB port, but following the reports I read it isn't a real difference to USB 3 (just about 50 MB/s more) - that's not worth the enormous difference of the price of a Thunderbolt enclosure compared to a USB enclosure.

    Anyhow, the external SSD isn't slow and much better than the original HDD, but the original SSD is three times faster than an external one.
    --- Post Merged, Feb 1, 2016 ---
    Check out youtube, there are several videos on booting an iMac from an external SSD - you just have to search a bit. Videos on booting from the original HDD are scary...
  6. maflynn Moderator


    Staff Member

    May 3, 2009
    I understand and can sympathize with the budget constraints, but I'd look to maybe seeing if you can upgrade to the 2TB fusion drive or better yet the SSD - just my $.02

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