Using external ssd?

Discussion in 'iMac' started by MikeArtworks, Jun 4, 2015.

  1. MikeArtworks macrumors regular

    Jun 1, 2015

    Can anyone tell me if this will be faster than an 7200 rpm inside the iMac? I can't afford to spend 500 euros more (to get ssd upgrade), but I have a ssd here, and can buy a case.

    Also, do you guys know if I can use my 2.5 inch ssd, with a external harddisk enclosure, that is sata III and usb 3 powered? They are the same size, but in the name it says harddisk.

  2. dwfaust macrumors 601


    Jul 3, 2011
    The drive may be faster, but you will be limited to by the speed of the connection - USB3, Thunderbolt, etc.

    As far as the enclosure, yes, you can use it. AFAIK, there is NO SATA support on any MacBook/Air/Pro.
  3. joe-h2o macrumors 6502a

    Jun 24, 2012
    The drive will be faster and yes you'll be limited by the USB bus if you go that route - you don't say what year your iMac is so unsure if you have USB 2 or 3.

    Even with the slower external bus though, the big gains you'll see are in IO operations - actually accessing the drive. With no seek latency, it can access really quickly so you offset a lot of the penalty for not being on an internal bus.

    If you use USB3 or Thunderbolt though, the penalty is almost nothing anyway in practice.
  4. Fishrrman macrumors P6


    Feb 20, 2009

    You have USB3, is this a correct assumption?

    If so, it's VERY easy to add an SSD as "your external booter".

    It is IMPORTANT that you buy the right enclosure or USB3/SATA docking station.
    You ABSOLUTELY want one that specifically supports UASP (USB attached SCSI Protocol).

    With a UASP-capable enclosure or dock, you should get read speeds up around 430mbps, and write speeds of at least 240mbps.

    I have had good experience with both Intel and Crucial SSD's, and recommend that you consider one.
    I've also had good experience with this enclosure:

    There are some "ready to go" external SSD drives out there, but be careful about what you buy.
    The Samsung "T1" line looks decent (I have no "hands on" experience with these, but the customer reviews seem favorable, by-and-large):

    A bit of "organizational advice":
    You DON'T need a "high-capacity" SSD, and you don't need to spend more for one.

    I would think that for practical purposes, you'll get by fine with a 240-256gb drive.
    Keep the OS, apps, and your accounts on the SSD for fast performance.
    If you have LARGE libraries of pictures, music, and movies, you might want to consider keeping them on a platter-based HDD (could be your current internal drive, or could be another external drive). There's no need to store seldom-accessed stuff on the SSD if doing so is going to "use up its space".

    I'm using an SSD mounted in a "lay-flat" USB3/SATA docking station, and after two years of running this way, I'm still only using 46gb of space for my OS, apps, and accounts.

    One other, important word about the concept of "TRIM" insofar as it applies to SSD's.
    In my experience, although TRIM is supposedly useful, I've found it to be "much ado about nothing". That is to say, after more than two years of booting and running my Mac mini from a USB3 drive, I have experienced NO noticeable slowdowns at all. Even using benchmarking software, the speed is within 1-2mbps of my "original tests" when I first installed the drive.

    I predict that if you use an external USB3-mounted SSD as your external booter for the remaining life of your iMac, TRIM will NEVER become an issue for you at all...
  5. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    Just remember that USB uses a packet structure to transfer data, meaning it requires the sent packets of data to finish transmission before the device can receive more data. (Interfaces like FireWire and Thunderbolt stream data instead.) It's seemingly a minor point, but can impact performance and is why it's preferable not to run the OS off a USB drive.

    For most people, it's fast enough, but if you're one of those who do a lot of random I/O, USB isn't the way to go.
  6. koulmj Suspended


    Mar 18, 2013
    That's how I run my iMac, and I love it. gotta be careful though, if the enclosure gets dc'd, or looses power the entire system crashes.
  7. AlexJoda macrumors 6502a


    Apr 8, 2015
    And you can't boot from a USB drive with boot camp and you can't use TRIM with it. The I/O performance is even better with my external Thunderbolt drive (850 Evo mSATA) than my internal 250 GB rImac SSD
  8. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    Actually you can boot from a USB drive with Boot Camp, but the process isn't easy. I also forgot to raise the inability to TRIM point, so thanks for bringing that up as well.
  9. ixxx69 macrumors 65816

    Jul 31, 2009
    United States
    This is where "experienced" users consistently misunderstand the vast majority of "typical" users. You are in the 5% who thinks this is easy. The other 95% would disagree with you.

    Likely the reason TRIM hasn't been an issue for you is because you're using so little space on your SSD. Without TRIM, as the SSD fills up, and then stuff is deleted, that becomes a serious slow-down. It's not "much ado about nothing" unless you never come close to filling up the SSD.

    Good advice though on the enclosure, etc. I paired an Inateck UASP USB3 external enclosure with a Crucial BX100 (500GB), and it's pretty decent - can peak ~350MB/s on both reads & writes. Keep in mind that the smaller capacity drives are often slower.

    Also yjchua95 is right on about USB3 - it's not a good interface for lots of random I/O. It's fine for streaming an itunes library, or copying a file. As soon as it has to handle something like an OS, it can get really bogged down, especially if there's other USB devices sharing the controller. That's what all those USB3 SSD benchmarks miss - they're always testing sustained transfer speeds (e.g. copying a large file or something simple like that).
    Not only is it not easy, but you can run into all sorts of issues related to software that uses hardware for license activation, which is pretty common in Windows.

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8 June 4, 2015