Drives - Internal, External SSD, DIY Fusion, Oh My!

Discussion in 'iMac' started by TheRealDanM, Feb 13, 2014.

  1. TheRealDanM macrumors newbie

    Feb 13, 2014
    Hey guys! I'm a longtime PC user and recently went to "the dark side" when I was given a 13" rMBP for work back in November and was instantly smitten with Mac and OS X. Being an old Unix guy, I just love being able to go to Terminal and really see what's going on. The OS X GUI took a little getting used to, and I'm still working on keyboard shortcuts, but I'm getting there.

    So, anyways, after a few months of using the laptop, I was ready to go the Mac on my home desktop. I was originally planning on going with a Mac Mini and using the existing dual 24" monitors I already for the PC and saving a few bucks, but I really wanted something with the Haswell processor and I got tired of waiting for the Mini to refresh. After weeks of contemplation and research, I was ready to pull the trigger on a 21.5" iMac, but when the time came to make the purchase, I just couldn't wait for Apple to build the system for me and I had to pick something up *NOW*! :D I walked out of the Apple store with a 27" iMac, knowing full well I'd be able to upgrade the RAM myself (which I did, quite easily). Unfortunately, that meant no SSD or Fusion drives, so I went to work on checking out my options.

    Having only had this monster of a screen sitting on my desk for one week, I wasn't ready to pull it apart and attempt to install an SSD myself (but, maybe next year...), so I decided I'd pick up an external SSD with Thunderbolt support and see what I could make it do. There aren't a whole lot of options out there, and they all run about the same price (depending on size), so I decided on the LaCie Rugged 120GB Thunderbolt/USB drive ( figuring the extra USB3 interface would give me some more options for this device in the future. I wasn't too keen on the bright orange rubber casing, but was pleasantly surprised when I received the unit that it easily comes off revealing a relatively attractive (if plain) brushed aluminum case.

    Next up was deciding how I really wanted to use this thing. I like the idea of the Fusion drive and letting the OS do the dirty work of deciding what belongs on the fast drive and what belongs on the slower drive. My findings with Blackmagicdesign's Disk Speed Test (using 5GB stress size), though, really surprised me....

    This is the stock internal 1TB 7200 RPM drive in the 27" iMac:

    The first surprise was the Write speed on the Thunderbolt connected SSD. Read speed was great - over double the read speed of the internal drive. Write speed, though, was just slightly slower:

    Next I created Fusion drive using the Thunderbolt connected SSD and the internal HDD using this great article from OWC ( Unfortunately, I somehow lost the benchmark details from the "clean" Fusion drive (with about 50GB of OS, Apps, and Documents). In my mind, that doesn't really matter anyways (in regards to determining Fusion performance) -- what is more important is what happens after you fill up that initial SSD and how the OS performs swapping data to/from drives and managing performance. So, I copied 200GB of misc. crap to the Fusion drive -- music, movies, pictures, etc. After that, Write performance fell through the floor, but Read performance still acceptable:

    (I ran the test immediately after copying the data, and approximately 8 hours after copying the data - assuming/hoping that the OS would optimize the data in that time. Probably a bad assumption, since I wasn't actively reading/writing the data, so OS X really doesn't know what is important and what isn't. Unfortunately, it would appear to assume that *everything* is important - at least initially - but still, 35.8MB/s Write speed? That's crazy slow!)

    OK, what happens if I remove that 250GB of crap (and empty the Trash)? One would think that, since only 50GB is being used, the OS would go back to using the SSD first. Apparently not.... (again, after an 8 hour wait...)

    It got even slower -- both Writes and Reads, and rather significantly slower than the stock drive. In my mind, that's simply unacceptable. But what does this mean? Many people have speculated that creating a true Fusion drive with an external device is not possible. My tests would seem to prove that. I'd love to see how my tests run on a true Fusion drive.

    Armed with this information, I'm going to run with the Boot and System files from the External SSD and use the internal drive for User files. This has been a great learning experience for me, a perfect opportunity to really learn the ins-and-outs of TimeMachine (and SuperDuper, which was a much faster backup/restore option), building boot devices, installing OS X, etc. Hopefully this will be of some use to others out there.

    Desc						Write	Read		Link
    Stock Internal 1TB 7200 RPM Drive		170.1	181.5	
    External Thunderbolt LaCie 120GB SSD		162.1	382.6
    DIY Fusion (Thunderbolt/Internal) - 250GB used	35.8	227.6	
    DIY Fusion (Thunderbolt/Internal) - Cleaned Up	30.6	165	
    External USB3 Matsunichi 1TB			73.1	73.1
  2. hfg, Feb 13, 2014
    Last edited: Feb 13, 2014

    hfg macrumors 68040


    Dec 1, 2006
    Cedar Rapids, IA. USA
    Hi ... and welcome to MacRumors forums! :)

    Although the DiskSpeedTest is widely used here for performance comparisons among different users, it isn't the best test for SSDs. However, since it is easily obtained, free, and provides a consistent "yardstick" for all users, it is a useful tool for comparing drives, enclosures, and interfaces here.

    The Lacie "Rugged Thunderbolt / USB 3.0" is one of my favorite enclosures and performs quite well. The unit I bought new with 256GB SSD (I also have several refurb units which I swapped the hard disk for SSD) used a SanDisk SSD which I didn't find to be the fastest around, but certainly adequate. Put a Samsung 840 Pro in that enclosure and it really flys!

    There are several SSDs whose controller (i.e. Sandforce) doesn't do so well on writing tests with the DiskSpeedTest due to the use of non-compressable test data. Although they may read low on the test, they still perform well with the small file random access incurred when running OS X.

    The DiskSpeedTest tool also doesn't appear to do so well with Fusion drives due to the test file size and the write algorithm used by Fusion which causes "hard disk" type speed readings.

    So ... I would only use the Test results as a general guideline, and rely more on how the system "feels" to you when running it day-to-day. The Fusion drive will take awhile to determine your usage habits and configure your programs and data to optimize your experience, so don't get impatient right away. :) Fusion is a compromise solution, but seems to be a good one for the very reasons you outlined in your post.

    Hope you enjoy your new iMac and DIY Fusion drive.


    Oh ... and you should obtain TrimEnabler and enable the trim function for your SSD in OS X

    Also, the LaCie "Rugged" is one of the few Thunderbolt enclosures I have found which seem to work well as a external Windows boot-disk (BootCamp like) if you want Windows on your iMac as well as OS X.
  3. MacsRgr8 macrumors 604


    Sep 8, 2002
    The Netherlands
    FWIW, I got the LaCie 1 TB SATA III Thunderbolt Little Big Disk (from the Apple Store) and have configured it via Disk Util in a RAID 0 (striped, 2 x 512 GB as 1 TB volume) config.

    It's nice and very fast, but the cooling system is a bit noisy....

    Below are my speedtests with it.

    Attached Files:

    • SSD.jpg
      File size:
      235.5 KB
  4. marzer macrumors 65816


    Nov 14, 2009
    That seems abnormally slow given the capabilities of the individual devices. A couple months ago I built a Fusion drive using a USB3 Seagate 1TB Backup Plus portable hard drive and a Samsung 830 SSD connected via a Seagate TBolt portable adapter. The Blackmagic benchmark was within 10% of the iMac's factory installed Fusion drive. I can only guess YMMV based on the combination of devices and adapters.
  5. rbart macrumors regular


    Nov 3, 2013
    I have exactly the same results with my Lacie Rugged 120Gb configuref as Fusion drive with my internal 7200rpm HD ...
    When I use my Mac, it's fast, and I don't feel the slow write performance.
    I know that the Sandisk U100 SSD into the Lacie enclosure is really bad in some tests.
    I plan to replace it with a Samsung 840Pro 256Gb to see if it performs better.

    In my current setup, it performs quite well just after setup, and then it slowdowns when I add more and more data.
    I think there is a problem with U100 sandisk when it's almost full.
  6. tennisguy macrumors newbie

    Apr 5, 2014

    Did you find a solution? While I don't have the best pre-fusion tests you do, my story is below. It is similar and I am trying to figure out why the speeds don't measure up to the drives I have.

    Hi all. I have a 3.2GHz i5 w 24 GB of Ram. Purchased in January 2014.

    My good friend helped me install a DIY Fusion. I purchased a 256GB Samsung 840 Pro SSD and he did the work to "fuse" it with the regular 1TB HD the iMac came with. It is attached via USB 3.0 in an OWC case.

    Originally, after being set up - Black Magic Speed tests benched it at 250-350 write and 500-650 read. I'm not a techie, but spent enough time to know that is pretty smoking and well above a typical disk hard drive.

    Well, now it is down to 70-80 write and 180-250 read. The imac still boots in less than 25 seconds, so I don't feel the system is slow. (and it certainly blazes next to the first generation aluminum iMac I had before - a 2008 model). But I am concerned at deterioration of speed and really thought the extra investment would have led to faster sustained speeds.

    So my questions are:
    * Does anybody have any ideas why this is happening?
    * Any idea what the fix is? I'm hoping not to have to start over.
    * Any ideas whether it would have been better just to keep the 256 a boot drive for OS & apps, and leave the 1TB for media? I almost did this and wonder if it would have simplified things or led to better performance.
    * Any idea where to go from here?

    BTW, I know a little about TRIM, but I think my friend said the Samsung will handle that itself.

    Lastly, you can probably tell I know a bit ABOUT this stuff, but not much on HOW to do it. So regular maintenance and upkeep is not my strong suit.

    Thanks in advance for comments & suggestions.


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