Help to better understand Fusion Drive

Discussion in 'iMac' started by ventuss, Oct 1, 2013.

  1. ventuss macrumors 6502

    Oct 9, 2011
    People and reviews keep saying that if you don't reach the mark of 128GB SS, then you are going to have the full SSD experience. Now, why do I get a 1/TB storage space if not to fill in with all my stuff? Is Fusion Drive smart enough?

    Fusion Drive has 128GB SSD, that is used to storage the OS and frequently used Apps. Let's say my Apps take 40GB, Games 60GB, and media 200GB. Most of my Media'd go to HDD, right? same goes for games I don't play for months. Now what if I don't use anything for two weeks? I'm on vacations, browsing the internet and reading my email. Would Fusion Drive empty my SSD and let everything extremely slow when I get back to work? Or it would keep my workflow on the SSD drive? What about my Aperture/Lightroom pictures?

    Now imagine I got my new iMac with 1TB Fusion Drive. First thing I do is installing a few apps and games, and start transfering over 500GB to my 1TB drive, and I know the first 110GB or so will be lightning fast, then HDD will take over and I'm going to wait forever, it's ok though, one time transfer. My 1TB Fusion Drive is half full. What is going to happen when I start using my iMac? Will the Fusion Drive take much to realized that I was just migrating my files to the new machine and I don't want my media files on SSD, but HDD? How fast is it going to be?

    I keep going from SSD to FD and back, and I just realized only a small part of 512GB SSD would be used to benefit most folks, reason why some users consider 256GB SSD. Then again, there are some information that are not clear on reviews, things only a Fusion Drive user can tell us, and I hope they do, because I am btw worldsin a place where 512GB is more expensive than 3TB Fusion Drive. I want to know better about Fusion Driver's Brain.
  2. Apple fanboy macrumors Penryn

    Apple fanboy

    Feb 21, 2012
    Behind the Lens, UK
    I think you are way over thinking this. The stuff you use the most will be on the SSD, the stuff you don't won't be. As someone who owns a fusion drive I can tell you it is always quick. Opening apps, pulling up old files, it all just works.
    Buy one and you won't be disappointed.
  3. ventuss thread starter macrumors 6502

    Oct 9, 2011
    Reviews and conflicted users are driving me nuts. I first went with 3TB FD, couple of days later canceled my order and decided for 512GB SSD, and suddenly I realized I may be throwing my money for the same results.

    Reviews usually say great things about Fusion Drive, but some say "as long as you don't fill the SSD", or the HDD, you'll be the full SSD experience. Problem is, why is there a 3TB option?

    If I don't order the iMac today I'm going to regret.
  4. faxao macrumors regular

    Feb 20, 2008
    Milano, Italy
    I must say I share the same feelings.
    I have just ordered a 27" iMac i7+1TB FD and I am really tempted to cancel my order and opt for an i5 3.4Ghz+512Gb SSD instead, after reading so much about "being in full control" of your file system as opposed to let FD deciding where your data are stored.....not an easy decision
  5. bp1000 macrumors 65816

    Jul 7, 2011
    Fusion and OS simply attempt to put all apps and settings on the SSD.

    It also writes to first 4 GBs of anything to the SSD. This might be a movie rip.

    It isn't perfect at working things out. As your drive fills up it gets more picky about what goes on the SSD. It always leaves at least 4GB free. So once your drive gets past 128GB used it starts to get more fussy. The good news is it's clever enough to move the bulk low volume stuff off. However it will try to fill the ssd part up.

    When it's saturated if you install photoshop for example which is over the 4gb min space, part of the program will go on the ssd, part on the hdd.

    It is this OS management that people who spec the ssd only wish to avoid.

    So as you can see it will try to use the ssd as much as possible but it doesn't always get the management right. It may store data on there that wastes valuable space needed for programs. Generally it gets it right.

    If you want ultimate control get the 256gb for OS and apps and an external for data.

    Whatever decision you make don't full up the 512GB with music and movies. Chances are you will run out of space and you don't need 500MB/sec read speeds to listen to an mp3.
  6. ventuss thread starter macrumors 6502

    Oct 9, 2011
    I don't know if I believe in control anymore. In the end it all leads to speed =/ or not.. most user's apps and routine seems to keep inside 128GB frame. You know what? If I didn't know this forum I'd be less confuse.

    Robin Harris / znet said "Comments welcome, of course. While I'm happy with my 500GB SSD, I think I'd be even happier with 2.5" 1TB/128GB Fusion Drive."

    Few conflicted articles..
  7. JustMartin macrumors 6502a

    Feb 28, 2012
    ok - imho there's a lot of nonsense talked about Fusion and it does confuse people. It's very simple, basically a form of caching.

    Frequently used blocks of disk are kept on the SSD portion of the drive while keeping 4gb free for writing. So, in the normal course of events, the applications and data I access the most will be on the SSD. If there's something I don't use very often, it will be on the hard disk.

    For example. If I import a CD into iTunes, it will go into the SSD using the 4gb free for writing. If I don't play that music very often, it will get moved onto the hard disk. If I play it a lot, it will be kept on the SSD and something I don't use that often will be moved off to maintain the 4gb free.

    When it comes down to it, are you using 128gb of different stuff every day? Probably not, you're probably using a lot of the same stuff for longer periods. So, you will be effectively running from the SSD.

    As to those people who insist on managing the fusion process themselves because 'they know better' or 'fusion gets it wrong', well I hope they enjoy the time they spend on the process. Me, I'd rather get a machine to do it and it is such a simple algorithm, I can't see that it would get it very wrong.
  8. faxao macrumors regular

    Feb 20, 2008
    Milano, Italy
    I have one more doubt though.

    Say you have your internal 1TB FD backed up (cloned) on an external HDD/SSD drive (either USB 3 or TB) and one of the internal drives (128SSD or 1TB HDD) fails.

    Would you be able to retrieve all your data from the backup drive and use them without problems?

    I hope the answer is "yes".......
  9. ventuss thread starter macrumors 6502

    Oct 9, 2011
    So it doesn't matter I have 1TB on HDD and have been using only 60GB, my 128GB SSD will always be full or almost full no matter what, be it videos, games or whatever. If I don't ever reach 128GB, I'll have an SSD full of unnecessary data. That explain's a lot the DDS vs Fusion Drive.

    Let's say my 1TB is full.. it may be that Photoshop is partially on the HDD, because some unnecessary media has been sitting over there. Possible? Like it doesn't really free space on the SSD, but keep it full and swap data with the HDD. Possible?

    You want as much storage space as possible, and want fast drive, so you get best of both worlds with Fusion Drive, until you use start filling the HDD, while maintaining the SSD full of something, whatever that is. Right?

    Now a 512GB SSD will have everything fast, no limits or slowness to free space or going though 4GB space. As long as you have an external drive to save crap.
  10. bp1000 macrumors 65816

    Jul 7, 2011
    Not quite sure what your questions are

    Yes it will try to utilise the SSD as priority especially when all the data you have is under the capacity of the SSD. It will start choosing what to place on the HDD once you reach the capacity of the SSD but it will always leave 4GB free.

    The drive doesnt know what you are copying to it next so if you install something like photoshop, it doesnt know at that stage whether it will be a frequently used program. It does attempt to install everything in the applications location to the SSD but if it is full with media then yes you get the apps slit across drives.

    Either way, the drive will manage itself, once you have say 500GB on there it will be constantly moving data to get what it thinks best serves you i.e. you main apps, program files, meta data caches on the SSD. Some frequently used files like iphoto thumbs might also be there too, perhaps some music and the rest will live on the HDD.

    It's quite simple how it does it, it will manage it for you, that is all you need to worry about. Dont be concerned about what goes on the HDD. Most of it will be music, photos, movies, stuff that needs read speeds in the 10's not the 100's of MB/Sec. You will hardly notice any random access issues because of the slower HDD because most stuff managed by OSX creates a library cache which will still live on the SSD.

    For anyone who likes everything in one place a 1TB or 3TB Fusion is a great choice.
  11. topmounter macrumors 68020


    Jun 18, 2009
    FEMA Region VIII
  12. Romain202122 macrumors newbie

    Oct 1, 2013
    Hello, I just ordered an imac,my first one!!!!
    and I would like to understand a little more fusion drive, I took one that my Mac start faster and launch program like adobe premiere faster... But I have a iTunes library of 110 go and I don't want this space to be taken by iTunes.. Will it be ?
    (Sorry for my English)
    Thank for your help.
  13. bp1000 macrumors 65816

    Jul 7, 2011

    Fusion is good choice it will start apps faster

    iTunes will live partly on your ssd until more programs need the space, then it will auto move your library.

    It favours apps over library data but if under 124GB it keeps as much on the SSD as it can :)

    Always keeping 4gb free

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