Is it better to run MacOS off the provided Fusion Drive or off an external SSD?

Discussion in 'iMac' started by RamiroCubria, Jul 27, 2019.


Fusion Drive or External SSD?

  1. Fusion Drive

  2. External SSD

  1. RamiroCubria macrumors newbie

    Jul 27, 2019
    I just got a new 5k iMac. For specific reasons (living in a third world country and restricted time as i was on vacations) I had to get the 27 inch 5k base model. I did a 32 gb ram upgrade and bought an external ssd. Im currently running Mojave off the ssd with no problems, everything is pretty snappy and fast. I've hadn't had a single issue yet. But im wondering:

    The fusion drive is a 30 gb ssd (about 800MB/s read write) mixed with a 7200 rpm hdd. As I did not quite trust this Fusion Drive, I immediately installed mac os on the external ssd and im getting about 480 MB/s read write (samsung t5 500GB portable ssd).

    What do you guys think about what im currently doing? The SSD part on the fusion drive is quite faster (on paper) than my external ssd. And the OS is of course installed there.

    I do care about load times, and my heavy usage would be Final Cut Pro to edit video advertisements. I also pay close attention to the system snappiness. Do you guys think that running the OS on the fusion drive (in which the OS is installed on the fast ssd part) would be a noticeable difference than running it from the T5 external ssd? I have to say that im currently very happy with the system overall feel and speed.

    Thanks in advance,

  2. Trusteft macrumors 6502a


    Nov 5, 2014
    The fusion drive's speeds are in a way, fake.
    When the data you need to access are not preloaded on the SSD, the speeds will drop to the speeds of the mechanical drive and even slower.
    Hybrid drives are a scam as far as I am concerned.
    I don't know the size of the OS or how exactly it operates to know if the 30GB will be enough or not.
  3. nambuccaheadsau macrumors 68000


    Oct 19, 2007
    Nambucca Heads Australia
    And 32GB is just not enough to load all your apps and operating system as as above, the more you use the slow old 1TB platter drive, the slower the system will get. My SSD with system, apps but no music, movies or photos, comes it at 60.5GB.

    Used a Silicon PowerThunderbolt SSD externally on a 2011 iMac and it was great. USB3 is as fast, except for the boot procedure.
  4. JacobHarvey, Jul 28, 2019
    Last edited: Jul 28, 2019

    JacobHarvey macrumors newbie

    Apr 2, 2019
    I have just done a clean install of macOS 10.14.6. With no extra applications installed it is taking up 13.64GB of space so it should easily fit on the 32GB flash portion of a 1TB fusion drive with enough space for a few apps.

    Some people split the fusion drive into a distinct 32GB SSD partition and the 1TB HDD to make 100% sure that the OS and other important apps are installed on the fast internal flash but this isn't necessary for many users. Generally the system should feel similarly snappy regardless of whether you are using the internal 32GB of flash for the OS or the external Samsung T5 you have

    Some people have gone further and have upgraded the internal PCIe SSD to a bigger SSD and/or have replaced the internal SATA HDD with a SSD such as a Samsung 860 EVO. This obviously requires you to carefully follow instructions posted by others to ensure you don't break anything and voids warranty (so if you ever decide to do this it is best to wait until after your warranty has expired).
  5. CheesePuff macrumors 6502a

    Sep 3, 2008
    Southwest Florida, USA
    With 32 GB of RAM, even Apple recommends a 2 TB or above Fusion Drive (which has 128 GB SSD) since it will need to store all of that RAM data on the hard drive when it sleeps, and it will exceed the 32 GB of SSD space on the 1 TB drive, so yes keep the macOS install on the external.
  6. Fishrrman macrumors P6


    Feb 20, 2009

    Post read/write speeds from your fusion drive (use BlackMagic Speed Test).
    Post read/write speeds from your USB3 SSD.

    Let's see the results.
  7. Zen_Arcade macrumors regular

    Jun 3, 2019
    My 2 TB Fusion seems to be averaging ~750 MB/s write and ~2400-2500 read.
  8. RamiroCubria thread starter macrumors newbie

    Jul 27, 2019
    Thank you all guys for the quick responses! First time using MacRumors and so far I've had a great experience. For now I will keep running macOS of the external SSD. It's super fast and snappy and I haven't had a single issue (yet). If I ever experience some sort of issue I will make another thread to warn potential users of this method I used (a very old one indeed) of getting around the old HDD.
    --- Post Merged, Jul 28, 2019 ---
    @Fishrrman these are pretty accurate results of the SSD part in the Fusion Drive. Of course they are better than the T5 im currently rocking (about 500 MB/s read/write); but the t5 speeds are no joke either. So i think that the best option (at least for me, with my current OS an apps taking about 100GB), is to keep rocking the OS off the external drive.
  9. Fishrrman macrumors P6


    Feb 20, 2009
    The fusion drive reads at 4-5x the speed of the USB3 external.

    THAT'S what I'd be using to boot and run the Mac (at least for the immediate future).

    By using the USB3 drive as the boot drive, you are USING THE FAR SLOWER DRIVE.

    WHY keep doing it that way?
  10. RamiroCubria thread starter macrumors newbie

    Jul 27, 2019
    Yeah I totally get what you are saying. But the thing is that it is a super fast, but super small ssd (around 30GB). In my regular use; of using the system in both ways, I haven’t noticed a difference. I still have to start using final cut to see if there is a difference on performance. Im yet kind of figuring out what should I do. My OS takes about 100 GB with apps installed. Maybe I could run the OS off the Fusion Drive, while offloading the apps I want to load fast and snappy to the external SSD when those 32 gigs get full, which they will by the way, pretty quickly. Take also into consideration that the T5 speeds are no joke either and that it is a solid SSD.
    --- Post Merged, Jul 29, 2019 ---
    Maybe it boots a couple seconds faster; but it does not bother me at all. App launches and regular use is quick on the external drive too.
  11. RamiroCubria thread starter macrumors newbie

    Jul 27, 2019
    And also the thing is that given the internal super fast SSD is so small, I just would be able to install the OS there and maybe a couple of apps. But then, when it gets full, I will have to deal with the old HDD speeds, which do bother me. Also, as I sad previously, running the OS of the external ssd and the internal ssd makes almost no noticeable difference for regular use. Apps launch quick on both, file transfers are really quick on both (given the internal ssd is not full), and overall performance is really good on both. I really can't notice if apps launch 4 times faster on the internal SSD because on the external SSD they do launch instantly. And file transfers on the fusion drive, when the ssd gets full are really annoying.
  12. mikehalloran, Jul 29, 2019
    Last edited: Jul 29, 2019

    mikehalloran macrumors 68000

    Oct 14, 2018
    The Sillie Con Valley
    A Samsung X5 is the only external that will match the speed of that tiny 32GB blade.

    Booting from a SATA III SSD based external will normally be slower at first but as the HDD gets more full, only booting from the Fusion will be faster; everything else will slow down.

    The second your warranty is up, replace the Fusion array with a fast NVMe 3 x4 blade such as the 970 EVO. This is the same blade currently used in the X5.
  13. RamiroCubria thread starter macrumors newbie

    Jul 27, 2019
    Did not know of that one! Thanks a bunch!
  14. RamiroCubria thread starter macrumors newbie

    Jul 27, 2019
    @mikehalloran definitely added that X5 to my cart on amazon. Thanks for the recommendation!

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