1TB Fusion vs. 512GB SSD performance?

Discussion in 'iMac' started by iBighouse, Nov 24, 2014.

  1. iBighouse, Nov 24, 2014
    Last edited: Nov 24, 2014

    iBighouse macrumors 6502a

    iBighouse

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    #1
    I'm thinking of buying my first apple computer. It's not in my budget to pull out all the stops and go top of the line for all components. However, given the difficulty of upgrading CPU, video and the drive, I'm leaning towards 8gb of RAM, i7 processor and either 256gb flash or 1tb fusion drive.

    I will be likely running windows on the machine very regularly to run Revit. I am looking forward to running AutoCAD for Mac natively on it.

    I have been spoiled by the retina display on my ipads and iphone, so a non retina display isn't an option. I also qualify for an edu discount as faculty at a local community college so I can save a few bucks there.

    All of my recent work, and home, computers have SSD drives and I remember the pep that going to SSD made to those systems. I am concerned that the Fusion drive is just a gimmick and its performance might make me regret going back to spinning platters.

    Would I be better off with the 256 flash, or the tb fusion drive? I don't mind saving my data to a separate external SSD if it's all fast enough.

    Any Fusion Fans out there who have an opinion on my situation?

    Big Edit: I should have said the 256gb of flash, not 512...can't fix the title.
     
  2. Kritzmire macrumors member

    Kritzmire

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    #2
  3. iBighouse thread starter macrumors 6502a

    iBighouse

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    #3
  4. tillsbury macrumors 65816

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    #4
    Something to remember: Windows Bootcamp doesn't recognise the fusion drive, so you have to partition some part of the hard disk and run Windows with old-school spinning rust. In case you're intending to use Windows a lot.

    If you run it under Parallels you'll be ok.

    But beware of the benchmarks -- they read and write relatively small (under 128Gb) amounts of data, so they flatter Fusion drives as they are almost entirely using the SSD. In real life they are not so quick.

    Also remember a Fusion drive is similar to an unprotected RAID array -- you square the possibility of failure, so be absolutely sure of your backup strategy.
     
  5. iBighouse thread starter macrumors 6502a

    iBighouse

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    #5
    Thank you. You just settled the issue. Guess I will have to go with an ONLY SSD option.
     
  6. joema2 macrumors 65816

    joema2

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    #6
    Reading/writing up to 128GB of data is not small. The determining factor is not the ratio of cache size to data size, nor the amount of overall data read or written. Rather it's the "locality or reference": http://en.wikipedia.org/wiki/Locality_of_reference

    E.g, the L3 cache on the i7-4771 CPU in my iMac is only 8MB, yet it's accessing gigabytes of programs and data while maintaining a very high hit ratio. In any cache system, the cache size is much smaller than the underlying data, yet they usually perform very well. Fusion Drive is similar.

    For different drive types, the probability of failure is not squared. Rather it's the product of the two discrete failure probabilities. E.g, assume:

    128GB SSD annual failure rate = 1%
    1TB HDD annual failure rate = 3%

    Aggregate annual failure rate is given by the formula:

    1-(1-r1)*(1-r2), where r1=drive 1 failure rate in %, and r2=drive 2 failure rate in %

    1-(1-0.01)*(1-0.04)=3.97% failure rate

    In general SSD is pretty good, as long as everyone realizes the tradeoffs. Namely if the only affordable size is small and this forces frequent use of a slow bus-powered USB 3 drive, then overall workflow performance may not be any faster than FD.

    Also if important data is on the external drive, reliability is functionally no better than FD -- if you lose the internal SSD OR the external HDD, your workflow is halted.

    If a customer can afford an SSD iMac and a fast Thunderbolt external drive, AND the HDDs to back *both* of those up, then that's probably the best configuration.
     
  7. robgendreau macrumors 68040

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    #7
    I'd agree with that conclusion; remember for an riMac the Fusion or 256 are "free" with purchase. But I'd say that USB 3 would be OK for backup and maybe a clone if you need to be back up and running quickly (geez, maybe even a USB 3 thumbdrive these days). I don't see that there's much, if anything, to lose in choosing 256 Flash over 1TB Fusion. You're gonna have to have external storage of some sort anyway.
     
  8. tillsbury macrumors 65816

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    #8
    If the failure rates are similar, then the product of the two *is* the square. :cool:

    But you're right in your calculations if the failure rates are different. Whether we can know or trust failure rates of the specific drives involved is another question.
     
  9. qcmacmini macrumors 6502

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    #9
    My understanding is that all data on a fusion drive is stored on the spinner. So, if the SSD fails, you can replace it and 'restore' the fusion drive.

    Therefore the reliability is as good as the spinner.

    I'm no expert on this but I read a detailed article on the fusion drive and that was the way in which it described the system.
     
  10. robgendreau macrumors 68040

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    #10
    I'd love to see a citation to that. Fusion doesn't work like a user with a separate HDD and SSD; the user decides "hmm, I'll place that on the SSD because it's used often and puts an application or database there." Fusion works with blocks on the drive; it says "this block (and I do not care what it really is" gets used a lot so I'll move it over to the SSD." So you could have stuff the user would keep on the HDD on the Fusion SSD and vice versa. It's spanning the stuff at the basic level of the drive, not folders and files like we see them.

    Maybe TM could rebuild that mosaic. I dunno. "Data" is a broad term and includes prefs, application support, email libraries, databases at system level, and all sorts of stuff like that in the ~/Library. I wouldn't count on being able to boot from anything but the recovery disk if either part of a core storage volume went down.
     
  11. Cape Dave macrumors 68000

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  12. henriquede81 macrumors member

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    #12
    Fusion vs pure-SSD:

    I went for the Fusion (ssd+hdd) because it will be several times easier/cheaper to update the hdd part compare to the ssd one. In 2 years I would be able to replace the fusion's hdd by a 10gb ssd. About performance, the fusion is not compromising it so much in my point of view.

    I see the fusion drive much more "future proof", I'm not sure apple includes the hdd/ssd socket inside the iMac if you go for a pure-ssd.
     
  13. WilliamG macrumors G3

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    #13
    That is correct, as far as I'm aware. If you go SSD only, you don't get a bunch of parts needed to put in a 2.5" SSD down the line, which will set you back a bunch of money ($150+, as I recall). It's really very easy to open up the 2012/2013/2014 iMacs, and SSDs keep getting cheaper so in a few years time you can do that if you still need to.
     
  14. yjchua95 macrumors 604

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    #14
    Performance wise, the 256GB SSD will still trash the Fusion Drive in every way.

    The SM0256F SSD in my 21.5" iMac scores 650MB/s in writes and 720MB/s in reads.

    A Fusion Drive scores around 350MB/s in writes and 700MB/s in reads.

    I'd rather go for a small internal pure SSD and buy an external HDD. Less chance for internal parts failure.
     
  15. henriquede81 macrumors member

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    #15
    This is exactly what I'd call "not compromising" at all: writing 2x faster has nothing to do with "trashing"... at least in my dictionary. And about reading, the difference it is absolutely negligible.

    You are right saying that are less chance for parts failure but for me it is important to guarantee that I can upgrade it quite easily in the future.
     
  16. yjchua95 macrumors 604

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    #16
    *upgrade it quite easily*?

    Did I read this right?

    It doesn't matter whether it's Fusion or pure-SSD, both are going to be just as hard to upgrade when you've to pull apart the entire display to get to the hard drive bays.

    And besides, nobody makes Apple PCIe blade-SSD upgrade kits yet.
     
  17. henriquede81 macrumors member

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    #17
    It is much easier to update only the HDD drive (on the Fusion) to something else (SSD, quantic, etc...) in some years compared to the pure-SSD PCIe.
     
  18. yjchua95 macrumors 604

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    #18
    Care to explain how is it much easier?
     
  19. henriquede81 macrumors member

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    #19
    1) Check iFixit teardown, it's half process to reach the hdd compare to the ssd PCIe.

    2) It's much cheaper/easier-to-get a suitable hdd/ssd/whatever-technology to plug on this standard socket compare to the PCIe ... the PCIe stays untouched.

    Glad you are not disregarding a newbie's post anylonger, clear now?
     
  20. yjchua95 macrumors 604

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    #20
    Whatever it is, it's still far slower than a PCIe SSD. A 200 MB/s difference is very noticeable to people who do heavy 4K work (like me).

    No single SATA drive can top 700MB/s. RAID is another story altogether.

    And I did not say I will disregard it. I only said 'chances are that I will disregard it'. Which isn't equal to disregarding.
     
  21. henriquede81 macrumors member

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    #21
    OK, if you need top-speed, of course, you should ask for pure-PCIe-SSD but nevertheless 300MS/s is totally OK for 85% of the usage, I'd say...

    I'm very curious to know what would be the performance of an "custom Fusion" adding an nice sata SSD to the PCIe one. I will figure out about this in a couple years I guess.
     
  22. joema2 macrumors 65816

    joema2

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    #22
    How exactly would 200 MB/sec variance in *writing* rates make a "very noticeable difference" in 4k video work? Reads predominate writes by far, and the most time-consuming aspects are CPU or GPU limited, not I/O limited.

    I'm not questioning the *general* utility of SSD for video editing. In general I think SSD is better because you've got to have large external storage anyway, plus for optimal performance you must keep a lot of FD free space, which reduces its cost per gigabyte benefit.

    Outside of benchmarks, I just don't see the difference in SSD vs FD writing rate is "very noticeable" for typical video work.
     
  23. robgendreau macrumors 68040

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    #23
    iMac modification's not quite as easy as it seems, and I've taken apart iMacs. That gluing the screen thing can be a mess. And it voids warranty (which, if you had AppleCare, means they take care of the SSD/HDD failure for three years).

    And PCIe flash is the wave of the future, and faster than a SATAIII SSD. Which might not have TRIM either, and has hard to upgrade firmware, if it's Samsung. You'd get Fusion speeds by going a much easier route and just using Thunderbolt, and maybe even a RAID in a Thunderbolt case. Putting drives in an iMac just isn't as necessary as it once was.

    I dunno what you mean by "custom Fusion." There are instructions on how to turn drives into core storage logical groups out there. Unless Apple has changed something you could do that now.

    Future-wise, I see PCIe as becoming the norm in Macs. SSDs are dropping in price and will eventually replace all internal spinners I'll bet. I don't know that there is much point to making a logical volume out of PCIe flash + SSD. Maybe you should check with the nMP folks; if it was useful they would have done it. But I expect most go with SSD RAID instead along with the PCIe on the machine.
     
  24. mawyatt1 macrumors member

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    #24
    Would it be reasonable to get the base riMac with 1TB Fusion drive and later replace the 1TB hard drive with a larger HD? Say a 5 or 6TB, to create a 5 or 6TB Fusion drive? While I agree replacing the HD isn't simple, but something one somewhat skilled could attempt. If you did this how would the Fusion drive be created (formated) with the new HD and present SSD?

    Has anyone even tried this on any iMac?

    Sorry for all the questions, but seems like something that might work to start with the base riMac then upgrade later when the Fusion drive starts filling up.

    Thanks,

    Mike
     
  25. robgendreau macrumors 68040

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    #25
    I expect you could do this. Search on "diskutil coreStorage create" and you'll probably find instructions. I'm not sure if you have to use a specific brand/model of hard drive; in the past there were some issues with that in iMacs. I haven't seen anyone's write up of a replacement yet.

    But I have to ask why? 128MB flash and 6TB HDD? Most folks doing anywhere near that kind of storage are gonna invest in external drives, especially since you've gotta back that up somehow. And again, RAID via Thunderbolt is plenty fast enough for lots of stuff. Look at the nMP to see how the heavy hitters manage this; it's not too different with the riMac.
     

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