Trim on External SSD

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Trim on External SSD

Hi,

I recently purchased a Samsung T5 SSD and connected via USB-C, as I have a IMac (Mid 2017) with a mechanical drive. This is to improve performance - I set the External SSD as my System and boot drive.

I am just worried about the inevitable slowdown of the SSD write times due to no TRIM.

I have been reading a lot of posts over the internet about Trim for external SSD's (connected via USB 3.0 or USB 3.1 gen2). It is clear that Mac OS does not support the feature. Is there anything planned to accommodate this?

Regards,

Posted on Oct 11, 2018 1:00 AM

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Answer 1

Oct 11, 2018 10:22 AM in response to samtenor

TRIM can be enabled on a Thunderbolt SSD drive. I have done it

with my 2013 27" iMac with an SSD mounted in one of the old

Seagate Thunderbolt "sleds".

Since Thunderbolt is a subset (superset, I get them confused) of PCI-e,

the drive on this interface exposes itself as a SATA controller, just

like any drive connected internally. So, it basically transmits SATA

commands directly. It therefore allows the low level access

required for TRIM.

When a USB drive mounts, it is simply exposed as a mass storage device,

which does not contain any of the SATA command structure at all.

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Answer 2

samtenor

Level 4

2,074 points

Oct 11, 2018 5:13 AM in response to Agamajc

"A trim command (known as TRIM in the ATA command set, and UNMAP in the SCSI command set) allows an operating system to inform a solid-state drive (SSD) which blocks of data are no longer considered in use and can be wiped internally."

Therefore, USB interface SSD will not support TRIM, not matter what (Linux/Windows/Mac) operation systems.

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Answer 3

Agamajc Author

Level 1

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Oct 11, 2018 7:33 AM in response to samtenor

I purchased a Samsung T5 SSD - it is a USB type type C connection - sealed unit. So their is no way to do TRIM unless supported via USB 3.0/3.1.

Apparently the new drives do support garbage collection which is done automatically - hopefully that will be sufficient. In the meantime I will test my write performance every month and compare. Luckily my machine is not a write intensive system - I do not do any editing.

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Answer 4

Agamajc Author

Level 1

10 points

Oct 11, 2018 4:58 AM in response to samtenor

Thanks for the reply.

I guess that TRIM is not that important then if companies are producing external SSD, which by your explication can never be TRIM'ed.

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Answer 5

samtenor

Level 4

2,074 points

Oct 11, 2018 7:25 AM in response to Agamajc

For some situations, TRIM is essential - such as server or highly write/rewrite drives.

The USB SSD drives (mainly USB 3) do provide the easiest way to improve boot/read/write time.

I wonder thunder bolt interface (PCI-e architect) can achieve TRIM which I have not explored yet.

In the mean time, I took my chance and opened my Macs to put the SSD via SATA 3 interface for TRIM purpose.

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Trim on External SSD

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