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I am experiencing slow write speeds using an external Inatek USB 3.0 2.5" External Enclosure (UASP supported) with a Samsung 840 120GB drive. I just started using this setup on a late 2013 iMac as an external boot device. Read speeds are great at ~400 MB/s but write speeds are only 40 MB/s per BlackMagic. The disk is formated GPT Advanced with 4k. I'm not sure if the enclosure is defective or if its my configuration. Amazon reviewers of the enclosure report great read/write speeds so I'm not sure what to think. Any suggestions would be helpful.
The enclosure: Optimzied Inatek Enclosure
themacfreak
Posted 2014-05-12T23:12:56.037
Reputation: 73
The drive supports
TRIMwhich speeds up write times significantly, but I'm not sure a USB 3.0 interface will. The drive itself is fairly average in terms of 4k write performance, though. – Nathan C – 2014-05-12T23:19:11.870@NathanC Yes TRIM doesn't seem supported over USB 3.0. Would not using TRIM make up for such a big difference in speeds? Usually I get about 350 MB/s write speeds with this drive. – themacfreak – 2014-05-12T23:25:43.950
From the research I've done with this question, it sounds like the interface can make a huge difference in terms of performance. I bet if you were able to plug this directly into the machine (which you can't because coughapplecough) it'd be much faster. – Nathan C – 2014-05-12T23:53:36.110
It depends a lot on the age of the SSD and its history. If you use it without TRIM long enough, the write speed drops to equal the erase speed. Overprovisioning can help a bit. (Did you do that?) – David Schwartz – 2014-05-13T02:52:23.157
I have always used it with TRIM and disk is over provisioned with a 11GB partition but I'm not sure if its being used correctly over USB 3.0. – themacfreak – 2014-05-13T10:18:56.303