Trim support over USB C 3.1

PJivan

macrumors 6502
Original poster
Aug 19, 2015
456
431
So trim support was not supported by USB controller 3 of the old iMac and only via thunderbolt 2.
Now there are 2 ports thunderbolt 3/USB C 3.1, question is, does the TRIM support works for USB-C?
 

EugW

macrumors 604
Jun 18, 2017
7,313
4,694
TRIM is supported over USB but the controller for the drive has to support UASP.
I'm not sure that is enough, but where do you see UASP support listed? For my Samsung 850 EVO with USB 3 UASP-compatible SATA dock, I still get some serious slowdowns with heavy use. As in down to less than 1 MB/s speeds in extreme cases. If I let it sit for while, the speeds return. I'm guessing that TRIM is not working here (and I don't see TRIM support listed), and it's just taking its time with garbage collection. Does that make any sense?

I don't see UASP mentioned in the system report though. Does that mean I'm just not getting UASP support? I am thinking it must though, since I'm getting speeds of 430 MB/s on a clean drive over USB 3, which I didn't think was possible without UASP.
 

DeltaMac

macrumors G3
Jul 30, 2003
9,537
2,304
Delaware
No, UASP provides support for the much-higher speed that an SSD offers - but does not provide trim support. It's still a limitation of the storage support on USB.
You do have to decide if trim is really that relevant now (and is a hurdle that everyone must leap over)
Not everyone agrees.
 
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EugW

macrumors 604
Jun 18, 2017
7,313
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No, UASP provides support for the much-higher speed that an SSD offers - but does not provide trim support. It's still a limitation of the storage support on USB.
You do have to decide if trim is really that relevant now (and is a hurdle that everyone must leap over)
Not everyone agrees.
OK that makes sense. My dock is UASP enabled, and I do get higher speeds, but I see no evidence of TRIM support.

And I think it matters, because with heavy usage on a somewhat full drive, speeds can slow to a crawl. Thus, if I were ever to go to external storage on my iMac, it would most definitely be Thunderbolt. Unfortunately though, I don't have that option with my MacBook. Too bad the MacBook does not support Thunderbolt. When does Intel add it for Y series machines? 2019?
 

Weaselboy

Moderator
Staff member
Jan 23, 2005
29,180
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TRIM is supported over USB but the controller for the drive has to support UASP.
Not exactly. Here is an older post of mine that explains a bit.

You are correct. USB cannot pass along the SATA TRIM command.

What some people have read and it has caused confusion, is some UASP (USB-attached SCSI protocol) enclosure chipsets can convert the SCSI Unmap command (similar to TRIM) to TRIM commands at the drive. Windows can run this SCSI Unmap command with the Powershell command Optimize-Volume and the -ReTrim option. OS X cannot run the SCSI Unmap command (at least not that I have been able to find). So at this point, no matter what chipset you use, you are not going to get TRIM over USB on a Mac.

There is some discussion at the bottom of this article.
 
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