External Bootable SSD Late 2015 iMac

Discussion in 'Buying Tips and Advice' started by plasticbag01, Jan 22, 2019.

  1. plasticbag01 macrumors newbie


    Jan 22, 2019
    New York
    Hi All,

    I'm looking to buy an external SSD and make it bootable for my late 2015 iMac. I'm open to any suggestions, but I'm thinking of this as a single dedicated drive (I don't need multidrive units). It's a 5k display, with USB 3 and Thunderbolt 2 ports. I'm looking for the fastest option available as it's going to a boot drive.

    Thunderbolt 2 wasn't wildly popular and I'm having a hard time finding any drives, am I wasting my time? I don't mind putting drives into other enclosures, it doesn't have to be one stop shopping.

    If anyone has had any success (or failures) with the above request please let me know. Any additional advice as well would be great.

    Thanks in advance!
  2. jmiddel macrumors regular

    Mar 3, 2010
    Land of Enchantment
    USB-3 will be fine, so just get a SATA to USB-3 adapter and an appropriately sized SSD, clone the internal to the external using CarbonCopyCloner and you’re good to go.
  3. ChrisA macrumors G4

    Jan 5, 2006
    Redondo Beach, California
    Buy a USB 3 SSD. Format it as APFS, install MacOS then use Apple's migration assistant to move you data and apps. Then change the default boot drive and reboot.

    After using your new system long enough that you are sure there are now problems. and ADTER the first full Time Machine backup, then, erase the Mac Internal drive, make it also APFS and use it for storing bulk data that dose not need to be on the SSD.

    The above is exactly what I did with my iMac. Also if you have no already done so install as much RAM as will fit the the iMac, just max it out.

    YouTime machine backup drive does not need to be USB 3, it can be slow but you may as well use USB 3. Make sure this TM drive is at least 2X larger then al to data you have or will have

    I would not erase (aka "reformat') the internal drive until after you are running a few data on the external SSD and Time Machine has finished it's first complete backup of the new SSD. Maybe even wait until our cloud backup is done? (If you don't have this, sign up for it. Backblaze is only $5 per month.)

    One issue is keeping a usable backup while you make the switch. You have your old data i-on the old drive and I presume a Time Machine backup of this. To avoid accidents, unplug the tm drive and lock it in a drawer until after the transition is complete. This will prevent human error which is easier than you r think to do. Put the old TM drive is your desk at work, or see place far away. Buy a new TM drive for your new setup.
  4. plasticbag01 thread starter macrumors newbie


    Jan 22, 2019
    New York
    Thanks so much for the replies, I'm surprised Thunderbolt is not recommended. I thought it was a faster option than USB 3, which would be important given it's a boot drive. Glad to hear USB 3 works.
  5. Moonjumper macrumors 68000


    Jun 20, 2009
    Lincoln, UK
    While Thunderbolt is potentially better, price and availability gives USB3 significant advantages and only a small performance downside.
  6. weckart macrumors 601

    Nov 7, 2004
    I bought a cheap TB1 used drive and replaced the internal spinner for an SSD to use as the boot drive for my sister's 2015 iMac. The internal drive was a very slow 5400rpm. It wasn't that expensive to do. The main advantage is that TRIM is supported over TB but not over USB.
  7. the-bigwig macrumors member

    May 17, 2016
    Was in the same boat as you. Went with USB 3.0 enclosure with UASP support. What an improvement! About 370mbps/370mbps speeds versus 100mbps before. I suppose that's about 25% slower than Thunderbolt but well, you just can't notice it at all. The differences are imo not worth the cost of TB enclosure.

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