Thunderbolt 3/USB-c vs USB 3 speeds

[Ben Jenssen]

I'd like any advice on this;

On my Imac I have two TB3/USB-C ports and four USB 3. I have adapters on the two TB3 ports; one Apple w/HDMI, USB3 and TB3, and the other a Plexgear w/HDMI, 3 USB3, TB3 and SD card.

This way I can have two external displays connected via HDMI, and two fast OWC 6G extreme pro SSDs connected to TB. One disk for OS and the other for PT sessions and photo work. I use the 1tb internal hybrid spinner for storage. And a 2tb slow ssd usb for backup.

This works great. The displays are fine and the SSDs are quite fast enough to make the whole thing feel snappy. I measured disk read/write speeds on the ssds to about 400/160 mb/s. Practically the same if I connect them directly to the imac TB ports, instead of the adapter.

I'm simply wondering if anyone can tell me, if I was to get a new external ssd drive, do I have any potential to increase the speed? TB3 vs USB 3 and what kind of disk might I be looking for?

(My understanding is that with the 2017 21.5" it is pretty complicated and high cost to exchange the internal drive, and to increase the ram. Even though the memory is the weakest point of the system, I'm settled with it.)


Thanks in advance.

[JFreak]

If the external disk interfaces to TB3 you have no bottleneck there, but to get gigabyte speed the box needs to be able to take NVMe drive as in interface as PCI-express to the host computer. If it is SATA, then TB does no good.

[Ben Jenssen]

Originally Posted by JFreak

If the external disk interfaces to TB3 you have no bottleneck there, but to get gigabyte speed the box needs to be able to take NVMe drive as in interface as PCI-express to the host computer. If it is SATA, then TB does no good.

Thanks.
If as you say my TB3 is not a bottleneck, that means I could get more speed with the right TB drive? Can I have a NVMe drive on TB?

(I had my OWC ssds on a PCIe card originally, and there they mesured to 400/400 R/W mb/s speed, so I guess, with 400/160 on TB, it's the speed limit of the drives that I'm seeing. Write being slower on TB than PCIe.)

[JFreak]

If the TB box interfaces to host as PCI-express, then you can have thousands of megabytes per second transfer rates with the current NVMe drives. But if the box interfaces as SATA, then you are limited to SATA speeds.

SATA boxes are much cheaper, but if you want performance you need to find a box that is PCI-express (NVMe).

[JFreak]

Originally Posted by Ben Jenssen

TB3 is not a bottleneck

No it is not, TB3 can do 40 Gbit/s (5GB/s)

[Ben Jenssen]

Originally Posted by JFreak

No it is not, TB3 can do 40 Gbit/s

So I can just go out and buy a TB drive with faster I/O specs and plug it in?

(Clarification; I never considered a PCIe or SATA box, I had the ssds on a mac pro PCIe card, that's where I mesured 400/400.)

[JFreak]

I think your safest bet would be buying TB to PCI-express external chassis and install a PCI-express to NVMe storage card in there, this way you know for sure what you are getting. Guaranteed you can get gigabyte transfer rates that way, albeit it costs more than "TB3 SSD" that you need to find every smallest spec to find out that it really performs well.

[Sardi]

What SSDs are you currently using? That write speed is quite low. You should be seeing almost parity with read/write speeds even via USB3.

I just recently upgraded to a new Mac Mini so still using Samsung SATA SSDs in USB3 enclosures as prior to the new Mini, I was using a 2012 Mini. On the older Mini, I was getting almost parity on read/write. Eventually I’ll move to NVME drives now that I have 4 x TB3 ports.

But yeah, those speeds seem low.


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[Ben Jenssen]

Originally Posted by Sardi

What SSDs are you currently using? That write speed is quite low. You should be seeing almost parity with read/write speeds even via USB3.

As I said, they are 256gb OWC 6G extreme pro SSDs that I had on PCIe card in a mac pro, and I now have in TB enclosures. I haven't tested them with USB3, that's a part of my question to you here.

[Sardi]

Sorry. Missed that part.

So according to the website, you should be getting the following speeds.

TRANSFER SPEEDS1
559MB/S READ
527MB/S WRITE

That’s the type of speeds I get with my Samsung SSDs via USB3. Somewhere along the line, you have a bottleneck. It shouldn’t be the TB3 or USB3 ports although I’d try running them direct to the machine f possible and test the speeds. It’s possible the slow down is happening on the docks. If you’ve got the drive in a TB case, even TB1 will give you the above speeds.

Interesting to see where the issue lies.


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