Fusion Drive 128GB SSD with 1TB SSD

Discussion in 'iMac' started by Hexley, May 24, 2018.

  1. Hexley macrumors 6502a

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    Jun 10, 2009
    #1
    I originally have a 1TB Fusion Drive (128GB SSD + 1TB HDD) on my 2012 iMac. I was wondering if I can do another Fusion drive between a 1TB SSD + the original 128GB SSD will result in a higher throughput that will exceed 600MB/s R/W?
     
  2. casperes1996 macrumors 68040

    casperes1996

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    #2
    If the SSDs are not of very different speeds, there's no point in the Fusion Drive technology. You could use a RAID setup to "fuse" the two SSDs together and increase throghoughput that way, but that's different from a Fusion Drive.
     
  3. Hexley thread starter macrumors 6502a

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    #3
    Doesn't RAID0 require identical drives?
     
  4. wardie macrumors regular

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    #4
    Don’t think so but its very sensible as the striping will mean the pair only operates at the speed of the slowest one I believe.
    And of course if either fails you’re stuffed. Trade off speed for resilience. But that’s true of fusion drive too.
     
  5. casperes1996 macrumors 68040

    casperes1996

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    #5

    From Wikipedia about RAID 0
    A RAID 0 setup can be created with disks of differing sizes, but the storage space added to the array by each disk is limited to the size of the smallest disk. For example, if a 120 GB disk is striped together with a 320 GB disk, the size of the array will be 120 GB × 2 = 240 GB. However, some RAID implementations allow the remaining 200 GB to be used for other purposes.



    In other words; You'll get two partitions. One really, really fast that uses both drives simultaneously, and one partition that is just the big 1TB SSD's remaining storage. If you want to make it seamless, you could then fuse those two partitions into one Fusion Drive, where the Fusion Drive would consists of two partitions rather than two disks, with one partition being split among two drives.

    Striping does not limit speed. That's in fact the opposite of the effect of striping. It does however limit storage volume to double the smallest drive for the RAID volume. But the remaining storage can still be accesses, just not sped up by the setup.
     
  6. wardie macrumors regular

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    #6
    Re speed...Of course it increases speed vs a single drive but surely you're ultimately constrained by the speed of the slowest drive in the RAID0 array to retrieve its blocks? If you had an SSD paired with an HDD for example. Hence everything I've read says use matched drives so the performance is balanced. If you have two drives of both speed A say then performance is going to be roughly 2A but if you if you have drives of different performance A and B are what are you saying the increase in performance is when they are RAID0'd for read and write?
     
  7. casperes1996 macrumors 68040

    casperes1996

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    #7

    I had just written a large blob of text about the advantages... Then I got to a section I had titled "Concrete examples", and i started doing maths, and I realised that you're absolutely right. There are edge cases where you could still get an increase from the RAID - for instance if you're limited by how many reads/writes the CPU can issue over a single connection, but generally speaking you're perfectly right in what you're saying.

    I retract all previous statements I've made opposing this idea.



    The Fusion Drive idea still won't really get higher throughput than any of the individual drives either though. It just splits data between the drives so the fastest of the two gets the data that requires the most speed.

    So JBOD'ing it may work just as well really if the performance gap isn't very big.
     
  8. ignatius345 macrumors 68000

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    Aug 20, 2015
    #8
    All things being equal, I'd probably do something (Fusion or RAID) to make the OS see them as one volume just for convenience if nothing else.
     
  9. wardie macrumors regular

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    Aug 18, 2008
    #9
    No worries. I was just trying to clarify what you meant. I guess the point to the OP is that RAID is a different solution than tiered storage using Fusion. RAID0 is striping across (normally identical) disks for performance

    Hexley - I think the short answer is yes you could do it and it may > 600MB/s for a combined 256GB RAID0 volume, but there are many things to consider.

    When you say make a new drive (say a RAID0 volume) out of your original 128GB SSD and a new 1TB SSD where are they both existing? Is the 128GB unit the internal unit and you plan to attach a 1TB SSD via USB3? Or did you mean put the 1TB SSD internally too and does that use SATAIII internally I would assume.Trying to figure out how fast a RAID0 set up may be has many variables including the drives' innate speed plus the interface & controller used.

    - is the 128GB SSD on SATA internally or PCIe directly (faster) - I don't know spec for that old iMac, but you can probably tell by a Speedtest on that storage on its own. You may end up being limited buy the speed of the SATA controllers internally/externally. Anything internal is likely to be faster than external especially if its on PCIe bus directly not via SATA. SATA III is limited to c. 600MB/s per drive. So maybe in theory you could be talking double that. But that may mean you not taking full advantage of the raw speed of the 128GB internal SSD on its own because you've coupled it with something slower. Maybe test them individually.

    - you won't be able to implement a hardware RAID controller (as you don't have one built in) but macOS supports software based RAID, allowing you to make a RAID0 out of 128GB SSD + 128GB of the 1TD external SSD. Then you'd be left with a separate volume of say 900GB SSD externally, as explained above.

    - but its complex set up and has peril, if you pull the USB3 drive out you lose your RAID array and can't boot etc., if the USB3 drive crashed you'd lose both your RAID volume and your extra volume. Backup backup backup.

    - do you really need that quick R/W large sequential speed that set up in theory would give you over using single internal SSD anyway, and a single external 1TB SSD separately? Main real world benefit of SSD is the random access thus very fast small file R/W access anyway over HDD.

    - if you really want to go down the RAID0 route maybe look at a USB3/TB based external hardware RAID enclosure and host multiple SSDs in it.

    - personally I'd just boot off the internal 128GB SSD and then keep your big stuff on a 1TB external SSD on. have an old Mac Pro 3.1 and used to set up all sorts of software RAID0 with SSD in the internal (SATA) drive bays in that. I found it fast yes but occasionally unreliable, random times it would not boot, array failed requiring a restore etc. I gave up not worth the hassle.

    - flash storage on the PCIe bus directly internally is the way to go for speed, I just tested by 2017 iMac with 1TB PCIe SSD internal and its 1820MB/s read and write, no RAID, no fusion etc. Just $ of course

    - if you really need super fast throughput bin the 2012 iiMac and go buy a iMacPro for $$$ :)

    Bit of a download but I hope that helps.

    Maybe check this out: http://barefeats.com/imac12d1.html
     
  10. Hexley thread starter macrumors 6502a

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    Jun 10, 2009
    #10
    128GB SATA SSD & 1TB SATA SSD will be internal.

    My worry is that the the dead 1TB HDD will cause problems with the other part of the iMac in the future and I already bought the 1TB SSD & iMac install kit. Would be a waste not to go on with the install.
     
  11. wardie macrumors regular

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    Aug 18, 2008
    #11
    Probably will - I have a similar situation with an old Mac mini with 2x drives in. Second one (non-boot) is now dead and it causes issues on boot up, as it tries to mount it I think and fails somehow. Takes ages and half the time the boot sequence messes up (not sure why) and I just get the dreaded grey no entry sign not apple logo. Couple of reboots and it works. If I can be bothered I'll take it out. I've not found a way to tell macOS at boot up to completely ignore it - anyone know?

    Incidentally as another idea for you I replaced the boot drive a while back with a 750GB hybrid drive (which is another solution you may want to look at, basically a bit like a fusion drive [not quite] but built inside a drive itself by the manufacturer, so the host computer just sees a normal drive).
     
  12. Fishrrman macrumors P6

    Fishrrman

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    Feb 20, 2009
    #12
    The concept of a "fusion drive" makes no sense when you're using 2 SSD's.
    The purpose of fusion is to "eke more speed" from a combined HDD/SSD setup.

    I'd run two SSD's as "standalone" drives.
    You might consider keeping both as "bootable" drives.
    And -- back them up separately.

    Then... if you have problems with one... the other is "right there and ready-to-go".

    If you fuse them... this option for a "moment of extreme need" won't be there...
     
  13. casperes1996 macrumors 68040

    casperes1996

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    #13
    Does make sense if the two SSDs are of vastly different speeds. Not all SSDs are equal. For instance, fusing a PCIe SSD with a mid-tier SATA one will still give a benefit. It's not the same as HDD/SSD, but the idea of using faster storage for more speed-sensitive data still makes sense in this scenario. Or with something like Optane.
     
  14. wardie macrumors regular

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    Aug 18, 2008
    #14
    Apparently so and you can do it however you like with diskutil core storage commands... I found an explain here, you just list the devices in tier order
    https://www.lifewire.com/setting-up-fusion-drive-mac-2260165
     
  15. SketchyClown macrumors member

    SketchyClown

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    May 24, 2007
    Location:
    Abbotsford, British Columbia, Canada
    #15
    I'd roll a Fusion drive out of them and see how it goes. If you like the speed, great, if not, then you can always go a different direction. I expect the performance to be very good however.

    When rolling your own Fusion, in the instructions, make sure you put the faster of the 2 first in the Terminal command "diskutil cs create..." The Apple SSD is PCI so should be the faster bet over the SATA. So if your original 128GB is disk0 and the new 1TB is disk1 it would be similar to "diskutil cs create Fusion\ Drive disk0 disk1"

    Slightly more detailed instructions here....

    https://www.macworld.com/article/2014011/storage-drives/how-to-make-your-own-fusion-drive.html
     
  16. BLUEDOG314 macrumors 6502

    BLUEDOG314

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    Dec 12, 2015
    #16
    I did this before out of curiosity and saw no advantage. My advice would be to use the 128 as the boot drive and to house frequently used applications, then have the 1TB for everything else.
     

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