Thunderbolt 3 to Thunderbolt 2 adapter

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Thunderbolt 3 to Thunderbolt 2 adapter

I have a 2013 Mac Pro. I am in the process of adding some NVMe external drives for backup purposes. In a standard USB-C enclosure, the drives don't run all that fast (around 350 MBps average write speed), because they are going through a USB 3.0 connection (using a USB-C/USB-A cable).

I picked up a couple of Thunderbolt 3 to Thunderbolt 2 adapters (Apple parts), in the hopes that speeds would improve some (the adapters are supposed to be bi-directional). However, the external drive does not mount. I am thinking that Thunderbolt does not provide power for bus powered devices like USB does. Is this the case? Will the adapter only work with externally powered drives?

Mac Pro

Posted on Jan 14, 2023 6:50 PM

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Answer 1

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den.thed

Level 10

91,522 points

Jan 14, 2023 7:22 PM in response to Wakko Warner

That is correct. Those adapters do not supply power in reverse to bus powered drives.

To be honest I’m a little surprised that they don’t run closer to 500 MB/s like the 2.5” SATA SSDs that I have in some USB Sabrent tool free enclosures.

Maybe try using a better quality USB cable between the Mac and the enclosures.

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Answer 2

Jan 14, 2023 7:12 PM in response to Wakko Warner

Tthe Apple Thunderbolt-3 <-> Thunderbolt-2 adapter supports ONLY genuine Thunderbolt devices on each side. adding adapters to other protocols like USB-C is generally NOT successful.

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Answer 3

Wakko Warner Author

Level 2

470 points

Jan 15, 2023 6:52 AM in response to Grant Bennet-Alder

The read speed is similar. I did move the drive from an Orico enclosure to one from OWC and the backup time did decrease (from 1.5+ hours to about 58 minutes). The Orico uses a Realtek controller, and the drive is a Crucial P3 Plus, which is rated to 4,200 MB/s write speed.

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Answer 4

Jan 14, 2023 7:16 PM in response to Grant Bennet-Alder

USB-3 should be allowing you up to 5 G bits/sec. or about 500 M Bytes/sec.

It is possible the bottleneck is not in the Bus but in the drive itself.

are Read speeds comprable? what are your Read speeds?

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Answer 5

Wakko Warner Author

Level 2

470 points

Jan 15, 2023 6:59 AM in response to den.thed

I have a 2.5" 2TB drive in another Orico enclosure and it runs about the same speed as the NVMe. I do get better speeds when I hook up a 2.5 using an external adapter from Sabrent (they don't make it anymore - part number USB-DSC7). I have another 2.5" 2TB SSD on the way, so I have to decide whether to put it into one of the other Orico enclosures, or order another enclosure from OWC. I also only have one USB-C to USB-A cable right now.

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Answer 6

Jan 15, 2023 7:09 AM in response to Wakko Warner

late 2013 Mac Pro was probably late because it was waiting for ThunderBolt-2 chips in quantity. That model and every ThunderBolt (1 or 2) Mac after it is ThunderBolt-2.

Cables are the same, the ThunderBolt-2 Controllers can combine both data pathways in the cable to get 20 G bits/sec instead of just 10 for ThunderBolt-1

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Answer 7

Jan 15, 2023 7:26 AM in response to Wakko Warner

Attaining speeds faster than about 3500 M Bytes/sec would require a PCIe-4 slot wider than x4.

Thunderbolt-3 connection provides comparable to PCIe-3 bus x4 slot, or about 2500 M bits/sec.

look at this OWC sales page for their 1M2 PCIe slot card with their (up to 3200 M Bytes/sec) 1 TB drive installed. Scroll way down for performance benchmarks:

https://eshop.macsales.com/item/OWC/SACL1M01/

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Answer 8

Wakko Warner Author

Level 2

470 points

Jan 15, 2023 7:50 AM in response to Grant Bennet-Alder

I am stuck with USB 3.0 and Thunderbolt 2. I do have a Thunderbolt 2 enclosure that has one 3.5" hard drive in it and a 2.5" SSD (mounted with a NewerTech AdaptaDrive caddy). The SSD is a 1 TB model from Eluktronics. That SSD tests at about 427 MB/s write, and 495 MB/s read, so it is much better. At some point I may be able to obtain a Mac Studio for a reasonable price, but it will be a while. Once that happens, then all of the drives should run much better.

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Thunderbolt 3 to Thunderbolt 2 adapter

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