Enable trim on TB external SSD Yes or No

[dimme]

I have a OWC thunder bay mini connected to a Mac Studio with 4 Samsung EVO SSD's. The connection is thunderbolt 3. I have had this setup for a while and it working OK. I just realized that trim is not supported. ChatGPT recommends I enable it through the terminal. But I thought I recall reading a while back that trim is not necessary on Samsung SSD because of Samsung's built in garbage collection. Any thoughts?

 

[Basic75]

If you can enable TRIM you should. Saying that garbage collection replaces TRIM is garbage, pun intended, because:

The drive's garbage collection needs to know which data is garbage that can be collected, and of the two ways how data becomes garbage, only one works without TRIM.

In other words, without TRIM your drive doesn't know what half the garbage is, and therefore can't "collect" it!

 

[PaulD-UK]

It may depend on what file system in use on the SSDs.
If you are using APFS:

Two important features of APFS are its Space Manager (Spaceman) and the Reaper.

• There is no documented need or use for trimming SSDs formatted in APFS.
• The trimforce command is inadequate, and may not work any more.
• APFS appears to automatically perform trimming on at least some SSDs when they’re mounted.
• Although I suspect that enabling trimming is no longer necessary for SSDs using APFS, there is no documentation that we can rely on to establish whether it might still be required.

Should you trim external SSDs?

Enabling the TRIM command was once thought important to maintain good write performance on SSDs. What has happened to it? Should we still be enabling it?

eclecticlight.co

 

[Basic75]

If you are using APFS:

The article you linked also concludes with "Recently, when I’ve been looking at how macOS mounts APFS volumes in disk imagesand Thunderbolt SSDs, I’ve discovered that Spaceman scans for free blocks and trims APFS containers when they’re mounted."

Even with APFS, if you delete a large file it's beneficial if somebody, the filesystem or the space manager, informs the SSD via TRIM that the data blocks are no longer valid, and consequently that the data blocks don't need to be preserved during write and/or wear leveling operations.

If I'm wrong please explain how and why.

 

[gilby101]

• There is no documented need or use for trimming SSDs formatted in APFS.

Apple TRIM the internal drive. To me that suggests that Apple see some benefit. The nearest we will get to documented need.

• The trimforce command is inadequate, and may not work any more.

I have never had to use trimforce. When TRIM is supported, it is run without any user intervention.

• APFS appears to automatically perform trimming on at least some SSDs when they’re mounted.

Yes, macOS performs TRIM at boot time on all SSDs which are capable.

• Although I suspect that enabling trimming is no longer necessary for SSDs using APFS, there is no documentation that we can rely on to establish whether it might still be required.

Same as first dot point.

I have a OWC thunder bay mini connected to a Mac Studio with 4 Samsung EVO SSD's. The connection is thunderbolt 3. I have had this setup for a while and it working OK. I just realized that trim is not supported.

I believe that is a limitation of the Thunderbay. But ask OWC. With any Thunderbolt connected SSD, the controller determines what is supported.

My limited experience:

1) Internal disk TRIMs at boot time.

2) My external Thunderbolt 3 SSD also TRIMs at boot time - with no intervention on my part.

3) It is a universal belief that all USB 3, 3.1, 3.2 can not be TRIMed with macOS. But/surprise, with Samsung software (a kext), my USB 3.1 Samsung T5 and T7 perform TRIM at boot time. TRIM rejuvenated the performance of the T7. I didn't test the T5.

To determine whether an SSD is being TRIMed, use this command shortly after reboot:
log show --debug --last boot --predicate "processID == 0" | grep trim
or maybe grep spaceman (a bit more output).

There will be lines like this if TRIM is being done:
2025-11-03 12:19:17.757450+1100 0x1872 Default 0x0 0 0 kernel: (apfs) spaceman_scan_free_blocks:4119: disk8 144153527 blocks trimmed in 759476 extents (489 us/trim, 2041 trims/s)

For my Samsung T7 that last line is 8 minutes after boot and login. In terms of trims/s it is 20 times slower than the internal and TB3 drives.