External SSD and TRIM

Discussion in 'macOS' started by Ceebler, Jan 4, 2016.

  1. Ceebler macrumors newbie

    Jul 4, 2007
    I just bought a new iMac (late 2015) with an internal 1 tb SSD as the main drive. However, I want to preserve as much space as possible on the drive, so I am considering using an external SSD to store my iMovie and Photos libraries. I want it to be an SSD so it is still fast, but I also was considering using a USB3 enclosure due to the cost of Thunderbolt drives or enclosures. I've read that USB3 doesn't support the use of TRIM. My question is, is TRIM necessary if my SSD is not a boot drive? If I don't have it, will it degrade the performance of the SSD in this application?

    Thanks for any help you can provide.
  2. Weaselboy Moderator


    Staff Member

    Jan 23, 2005
    It does not really have anything to do with being a boot drive so much as it is related to writing to the drive. Having TRIM on helps maintain write speeds if there is a lot of disk write activity, so TRIM is a good thing to have. That said, all drives have garbage collection built in to firmware that somewhat mimics what TRIM does in hardware, and ideally will keep write speeds up. Some people use SSDs without TRIM for long periods of time and see no slowdown while others so see a slowdown.

    Even if you do see a write speed slowdown, it does not permanently damage the SSD. If you attached it over eSATA or TB and ran TRIM'd unused blocks on the SSD, it would completely restore performance.

    I have a SSD in a USB3 enclosure I use for disk clones and I have not noticed and slowdown at all.
  3. Ceebler thread starter macrumors newbie

    Jul 4, 2007
    Thanks for the help!
  4. Fishrrman macrumors G5


    Feb 20, 2009
    If all you're going to do is "store" stuff like photos, movies and music on an external drive, you don't really need an SSD.

    A USB3 platter-based hard drive will "serve up" such things for viewing or listening fast enough when needed.

    Besides -- you spent all the $$$ for a 1tb internal SSD, might as well use it.

    What you REALLY need a 1tb external drive for is to back up the contents of the internal SSD.

    Insofar as TRIM is concerned, I believe we'll soon reach a point where it matters for little or nothing when dealing with externally-mounted USB drives.

    I've been booting and running my Mac Mini for three years via and SSD mounted via USB3 with NO noticeable degradation of performance, and TRIM has NEVER been used (can't be enabled via USB3). Still runs just fine -- like the day I first connected it!

Share This Page