TRIM support for external drives using SSD instead of HDD

Discussion in 'macOS Sierra (10.12)' started by iLearnMac, Jul 14, 2017.

  1. iLearnMac macrumors newbie

    Nov 20, 2011

    About TRIM support for external SSD:-
    1. Is TRIM supported for external SSD too?
    2. Is this by default or we have to do some setting manually?
    3. - For manual settings please point to direction of information.

    I am thinking of buying a Samsung EVO 250 GB SSD.
    Put this SSD into a proper case to work as an external drive.
    (Similar to just like we use the external HDD.) ​

    With current SSD prices, it is very attractive to use it this way:-
    1. Samsung SSD 250 GB 850 EVO : ~ $130
    2. Enclosure: ~$25

    Dedicated external drives using SSD hover in upper of $500 !!! Even here I am not sure of TRIM.

    Thank you very much in advance,
  2. Taz Mangus macrumors 68040

    Taz Mangus

    Mar 10, 2011
    For external enclosures, Trim is only supported using Thunderbolt connection, Trim is not supported for the USB connection (including USB 3.1). The exception to this is: which does support Trim over USB.
  3. robeddie Suspended


    Jul 21, 2003
    How would only one external ssd brand support trim over usb and none others? Trim is software enabled so if it can be done with the drives you listed, do they offer their own proprietary trim enabling software? And if so, would that software work witb other external usb ssd drives?
  4. DeltaMac macrumors G3


    Jul 30, 2003
    Trim is supported on Macs with Angelbird drives - because Angelbird uses firmware that replicates Apple's own firmware.
    Thus, Angelbird brand drives support trim by default on Apple systems, same as Apple factory SSDs - no software is needed for that. Angelbird is the only company that does, outside of Apple.
    For any other SSD suppliers - trim, when enabled, is available through the internal bus, and thunderbolt --- not USB.

    If enabling trim is important to you, then you will need to connect that SSD through a bus that allows that function. USB does not.
  5. Weaselboy Moderator


    Staff Member

    Jan 23, 2005
    Taz and I were talking about that in this thread. TRIM won't work over USB, so I think what Angelbird may have figured out with their drivers and app is way to use the Windows SCSI UNMAP command to accomplish the same thing as TRIM on macOS and they are just calling it TRIM. It is accomplishing the same thing, but I don't think it is really the SATA TRIM command.
  6. Taz Mangus macrumors 68040

    Taz Mangus

    Mar 10, 2011
    Angelbird provides their own app which probably is the one that communicates with their SSD. In essence, Angelbird is issuing the Trim commands to their hardware on the SSD. The Mac OS is not directly involved here. I think this is very clever and maybe even elegant solution.
  7. sneak3 macrumors 6502a

    Oct 14, 2011
    Hey folks. Sorry to ress this thread but I thought it was really interesting.

    I'm planning on using a couple of external SSDs for fast storage, CCC or even Time Machine.

    So if TRIM doesn't work via USB, does that mean the SSD will fail quicker than normally? Is there anything else I can do to prevent that?
    I heard that leaving a 25% partition free would be super recommended but that is only so that TRIM can work, right?
  8. treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    When data is written to a HDD, it just writes the data in one step. For a SSD, to write data, the sector must first be erased if it has data on it. From everything I've read, when a file is deleted on a SSD without TRIM, the sector isn't necessarily erased, with TRIM, the OS tells the SSD that the data on the sector is no longer needed and the SSD can erase it. Thus, when data needs to be written to that sector, the erase operation doesn't have to be performed because it's already been done. But the amount of write operations is the same in TRIM vs. non-TRIM and most believe that the number of write operations is the biggest determinant of the SSD lifespan. Thus, there should be no practical difference in SSD longevity between TRIM and non-TRIM. As for keeping some percentage of free space, all SSD manufacturers over-provision storage - keep some space free for failing flash storage. Once this over-provisioned storage is used, there may be some difference in what vendors do - if a particular SSD stops writing once the over-provisioned storage is used or continues to work until it can no longer write new data. In any case, TRIM or no-TRIM shouldn't make difference. If you're using a disk (HDD or SSD) at the system disk, you should try to keep more free space available. For my media HDD's, I go up to about 98% used.
  9. sneak3 macrumors 6502a

    Oct 14, 2011

    Okay thanks. But why the difference between system and storage?

    And I have read that SSDs with full numbers have no over-provisioning, like 1TB vs 960 GB. My samsung 850 has 1 TB.
  10. treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    The OS needs disk space to perform it's normal operations. Numerous applications may require non-trivial amounts of disk space as well even if nothing is ever "saved". For example, the video editing application may use gigabytes of disk for caching a video file before I ever save the project or export the video. Applications will typically use the Library/Application Support folder in the user's home directory for this purpose and while there are ways that one can redirect where these files are written so they're not written on the system disk, most people won't take the time to try to manage disk space at this level of detail. I don't - I just make sure I don't fill the system disk to the point where it may become a problem. If you run out of disk space on the system disk and the OS needs the space, it may get to the point where the system can no longer function.

    Actual data files which you may store on a non-system drive tend to be more predictable (of course, this varies from person to person). Also, if you run out of space on a non-sytem disk, you'll get a message of no more space but that doesn't affect the OS's ability to run.

    I have not seen that the number of zero's in a SSD's capacity indicates it's over-provisioning size. Samsung SSD's usually have sizes like 250GB vs. 240GB for other manufacturers, 500GB vs. 480GB, etc. But it's my understanding that they factory over-provision all their consumer drives - 7% is one figure that I see. The NAND chips used is a big factor in the SSD capacity. The Crucial MX300-series SSD's have more capacity (275GB vs. 250GB or 240GB from other manufacturers, for instance) because of their NAND chips. I'm not aware of non-Micro/Crucial consumer drives which use the Micron NAND chips so you don't see other SSD's with this type of capacity. Similarly, I don't think Samsung sells their NAND chips to other consumer SSD companies (they sell OEM to computer companies like Apple obviously). Publicly available tech specs regarding factory-set over-provisioning seems to be scarce. Mac users are not likely to manually change factory-set over-provisioning (even if it's possible) because SSD manufacturer software which does this usually doesn't run on the Mac.
  11. sneak3 macrumors 6502a

    Oct 14, 2011

    Wow that was a hell of an explanation. Thank you so much for enlightening me ;)

    Everything makes sense now. I think people were just plainly guessing that SSDs with lower capacity had over-provisioning then.

    Which is all great cause I was about to partition 100 GB out of my 1TB samsung 850 (used for storage) cause I thought it would significantly increase performance/durability :)
  12. treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    I have seen the suggestion to allocate a partition and not use it as a means of over-provisioning on a SSD but I don't know why people believe that helps in current SSD's. Unlike typical HDD's, SSD's has a fluid concept of sector locations. As mentioned earlier, the major determinant of the lifespan of a properly functioning SSD lifespan is the number of writes. In order to spread the number of writes throughout all the blocks of the NAND chip, the SSD controller will not write 100 times to the same block if there are other blocks that have not yet been written to (wear leveling). So even if one creates a partition (through the OS) which isn't used, the SSD controller will not be constrained to observing this limitation. It will wear level through all the NAND blocks. If you have SSD management software that can control the over-provisioning, you can do this, but I doubt that creating an empty partition will over-provision a SSD. Now, if somebody doesn't keep track of disk usage and uses the empty partition as a way of limiting usage, I guess that would work for that purpose.

    The best way to increase SSD lifespan, other than making sure the physical environment is not detrimental to the SSD electronics, is to reduce the number of writes. But obviously, one can take this to an extreme. Try not to do writes that don't add value to your computing experience. So what that means for me is that my web downloads are done to a HDD since most of it (byte-wise) are video/audio files and program (Mac OS) downloads. My Internet connection is slower than the the HD speed and I store almost all my media on HDD's anyway and the downloaded program bundles aren't used after the installation is done. On the other hand, web browsing can require a lot of writes but do you really want to slow it down by having it done to a HDD? At the end of the day most people won't exhaust the write count of their SSD's before they become technologically obsolete, but by doing some planning, one can help ensure that this doesn't happen.

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