I'm about to purchase an external SSD enclosure (case) for my Samsung 860 QVO. Some case manufacturers mention "supports TRIM" in the description, some don't. Reading online, I only could find evidence that TRIM support is dependent on the drive that receives it and the OS that sends it. Could an enclosure with a cheap controller prevent the OS from performing TRIM on my drive?
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Yes, in theory it could.
The drive speaks ATA, while all USB storage devices speak SCSI – the enclosure's controller has to translate between the two command sets (and usually provide a special "ATA passthrough" command for things that don't translate well). It could certainly be that the enclosure does not know how to translate the SCSI 'UNMAP' command to the equivalent ATA 'TRIM' command and doesn't report the capability to the OS.
(I seem to also remember something vague about this command only being allowed in UAS mode, not in the basic BOT mode, but I'm not sure how true that is.)
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Yes, in practice it does.
It is rather hard to find an USB-SATA cable or adapter or enclosure that is capable of translating the TRIM command.
A colleague of mine was tasked to find a TRIM-capable cable (not enclosure) and they ended up buying about 6 or 7 different ones and testing them.
fraxinus
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