Fusion vs SSD

Discussion in 'iMac' started by TwoBytes, Dec 16, 2012.

  1. TwoBytes macrumors 68030


    Jun 2, 2008
    When you're over the 128SSD, how fast is the performance?

    I remember for audio work building computers with two drives. One fast drive has the OS one drive had audio samples and it sped performance up. Fusion is faster than regular HD as OS apps are there but is there any rough information out there for speed tests? IE SSD is xx% faster than fusion?

    Anyone done any comparisons? You'd need a computer with a pretty full fusion drive to do it though unless someone with a fusion drive here can comment how fast their system is compared to their old HD iMac?
  2. pokrface macrumors member

    Dec 14, 2007
    That's a complex question, and the best answer is probably "it depends."

    If you have less than about 110GB of stuff, you'll never use your hard drive and everything will stay on the SSD. In that case, your experience will be that Fusion Drive is SSD-fast, all of the time.

    If you have more than about 110GB of stuff, your most frequently-used data will end up being tiered to the SSD. If you've got a set of files you access regularly, those files will likely be promoted to SSD and stuff you access less-frequently will be demoted to HDD, so if you're going through a regular workflow with mostly the same applications and the same data files, they should end up on the SSD.

    It's impossible to predict how "fast" Fusion Drive will be after the SSD fills up and it has to begin promoting and demoting things. Indications are that whatever algorithm Core Storage uses to track frequently accessed chunks is pretty sensitive to that frequency and that it's pretty aggressive in keeping hot data on the SSD. Also, anything new you add should land on the SSD first, so if you're working with audio and you add a bunch of new audio files from external media to your Fusion Drive, those new files will wind up on the SSD first (and something cold will be demoted from SSD to HDD to make room for them, because FD strives to keep a minimum of 4GB free on the SSD).

    If, however, you really have >110GB of data and you need constant SSD-speed access to *all* of it, *all the time*, you'll probably notice quite a few hiccups as FD shuffles data around, with the hiccups occurring more frequently the more data you have. Someone with a monster-big Aperture library might run into this, for example (though I'd suggest to that person that they consolidate their originals onto an external drive or a network share to keep the library's size down).

    Your answer to this question will be different from someone else's answer, and there's just no way to know until you have an idea of how much stuff you have and what your access patterns are going to be like. There's certainly no useful way to quantify it, like, "Fusion Drive will be X% as fast as having a giant SSD," because the subjective "speed" of FD is totally dependent on what files are on it, how full the SSD is, and what you're accessing when.
  3. Yebubbleman macrumors 68030


    May 20, 2010
    Los Angeles, CA
    The Fusion drive acts like a glass of water on top of a giant bucket with water filling both of them up from up top (and with the overflow from the glass falling off and into the bucket), at least before it figures out what you access most frequently. I'd imagine performance on the OS and on the audio apps would be fast. Maybe on some of the samples as well. Otherwise, it's probably a lot like accessing files from a hard drive.

    Ars Technica, Macworld, and many others have speed tests with Fusion. You should look them up.
  4. TwoBytes thread starter macrumors 68030


    Jun 2, 2008
    Both very intelligent answers. Thanks for the thoughts.

    If FD keeps only 4GB free, downloading a couple of HD films from iTunes could start causing hiccups.

    I have huge sample library's so FD will always be 'full' (minus 4GB which could be used pretty quickly in an audio or film project). I wonder how apple have accommodated for these users with FD..

    I don't know how people could settle for an 128GB main drive by not going over. That's what I had over 10 years ago.
  5. barefeats macrumors 65816


    Jul 6, 2000
    speed drop in Fusion when SSD overflows

    The Seagate Barracuda 7200.14 model ST1000DM003 1TB HDD is what shipped "fused" to the 128G SSD on my 27" iMac. According to the specs page on Seagate's site, it is capable of 210 MB/s "sustained data rate OD" -- whatever that means.

    I've measured the Hitachi 7K3000 7200rpm 2TB HDD in my Pegasus R4 at 150MB/s large sequential (QuickBench 1GB Custom Sequential Test).

    The WDC Velociraptor 10,000rpm 1TB HDD tested at 200MB/s large sequential.

    Even if the Seagate ST1000DM003 is capable of 210MB/s in the real world, that's about half the speed of the SSD. It's worse if you are transferring small random files. In that case, the SSD is at least 5 times faster than the HDD.
  6. leman macrumors G3

    Oct 14, 2008
    If you have professional demands of your storage (e.g. working with large audio, video or other data), you will have the best experience/reliability etc. working with an external disk array.

    Fusion Drive and tiered storage in general is great technology which learns your usage patterns and accommodates appropriately. However, the obvious assumption of this technology is that such patterns actually exist. This is certainly true for your 'normal' data such as OS, applications, contacts, ebooks, media library and what not. However, many professionals use data in a completely different way. I doubt that Fusion drive will be any slower than a normal HDD for any kind of access patterns, but it is certainly possible to use it in a way where it is as slow as an HDD.

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