What does USB 3.1 mean in System Information? Why am I not getting full speed on my SSD?

betaneptune wrote:

Which 3.1 is meant in the System Information USB panel? Gen 1, Gen 2 or either? Seems to me it should be more specific. I assume it's at least the 10 Gbps version, but maybe it means it could be Gen 1 or Gen 2.

It looks like Apple is choosing to using the "former name" for USB on purpose. It is even more specific than the "current" name. If you check the Tech Specifications page for your computer, it will show the exact value. For example, this page shows both "USB 4 (up to 40Gb/s)" and "USB 3.1 Gen 2 (up to 10Gb/s)".

But USB speed depends on both the bus and the device. If you actually plug in a device, then it will show the speed of that connection. When I plug in an external, System Information reports "Speed: Up to 10 Gb/s".

At the others have mentioned, there are a lot of things which can affect the speed of any drive, but SSDs tend to have some additional things which affect the speed due to how the components within the SSD itself.

The software you have open and running can affect performance of external drives. Other externally connected devices can also impact performance of drives as well since they may sometimes interfere with each other due to compatibility issues...or maybe the system is transferring data to both devices at the same time even when they are on different busses. When testing an external drive always disconnect all other devices and make sure the drive is connected directly to the computer.

SSD specific issues are (especially for writing to an SSD....reads are usually fast although the following items can affect read speed as well at times):

• Amount of free space on the drive (not the volume)
• How much data has recently been written to the SSD. SSDs today are made with very slow NAND (TLC or QLC) so SSDs usually have a small write cache which generally only takes between 30seconds to 60 seconds to fill, but allows the SSD to write at/near the advertised speeds. Once the SSD's write cache is filled, the SSD's write speed may drop a small bit or even significantly. Sometimes it will take the SSD a long time minutes to an hour to recover the write performance.
• The size and amount of data also plays a role as does whether the data is for a single file or multiple files.
• The type of file system can affect the results.
• Most SSDs today may ship with different internal components including controllers which can sometimes significantly impact behavior & performance. Many times the SSD manufacturer's will not even provide a different part number for these variations so we cannot be sure what the SSD we receive even is. The manufacturer's are usually just providing a generalized performance metric these days.
• Benchmarks are made under ideal conditions. With SSDs I'm sure the benchmark was made by resetting the SSD to factory defaults before the benchmark was run, whereas you are testing the SSD after you have already used it (even just a little).

The values you are getting for the SSD's performance is close enough to the benchmarks since your are testing on a real world system and not an optimized setup for the best benchmark scores. Plus the cable and adapters used can affect things as well. These are just a few quick items I could think of off the top of my head.

"Envoy Pro" is just an OWC brand name. It essentially means little more than "OWC SSD". There are 29 different models of "Envoy Pro".

It sounds like you bought one of the USB models, not a Thunderbolt model. Therefore, it is never going to run at Thunderbolt speeds and you are stuck with USB versioning and branding.

betaneptune wrote:

The fine print says iMac Pro. So it's not apples to apples. I guess that's reasonable that I'm getting less speed: 7xx vs. 1002/992. Is that right?

The fine print is key on that page. For one thing, it says "Thunderbolt compatible". That should be a red light right there. It actually uses the word "Thunderbolt" 3 times on that page. But it's not Thunderbolt at all.

There are two screenshots on that page. The one for Blackmagic is much closer to your speeds. Any published result from those speed test apps should be considered suspect. For one thing, they always talk about video stuff and use absurdly large file sizes. 64 GB in this case. How many 64 GB files do you need to copy? Or have? Plus, it was a single file test. Any performance test on a non-embedded system like this should be considered invalid. You have to run several tests and take the average. But when advertising, they are more likely to run several tests and publish the best. Slight difference there. 😄

So in Sys Info, USB means 10 Gbits/sec? I guess it has to. It be nice if they were more specific.

In System Information, you have to find the device in the tree and it will tell you the maximum theoretical speed you can achieve with that device.

However, that may not be the device's actual speed, but the Hub you have it connected through.

Some USB 3 hubs will down-speed to USB 2 if there is a USB 2 device on the hub. I think it only happens if that is the first device connected.

For USB 3, you can match the generation and number_of_lanes – where if either is missing, it is assumed to be 1. Generation 1 = up to 5 Gbps per lane. Generation 2 = up to 10 Gbps per lane. So USB 3.2 Generation 1x1 == USB 3.1 Generation 1 == USB 3.0 == "up to 5 Gbps". (I hope.)

USB4 Generation 2 is not the same thing as USB 3.whatever generation 2. Both Generation 2s refer to speed of "up to 10 Gbps" per lane, but they are incompatible. USB4 has its own "up to 20 Gbps" USB transfer modes – and I believe at least one of those is mandatory for USB4 host ports. USB 3.2 Gen 2x2 is optional for USB4 host ports, and by all the accounts I've read, Macs do not support USB 3.2 Gen 2x2 ("up to 20 Gbps").

Apple Silicon Macs do support the optional USB4 40 Gbps USB transfer mode, and the optional Thunderbolt 3/4 ALT mode. But supporting optional 40 Gbps modes doesn't obligate one to implement an optional 20 Gbps one.

betaneptune wrote:

"They’ve worked for over 20 years to get the current level pf confusion. . "

LOL, too! (^_^)

20 years to keep "improving" on a dog's breakfast!

Starting with when USB 2.0 came out – promising speeds of "up to 480 Mbps", rahter than the "up to 12 Mbps" of USB 1. Do you know what the average user got if they went to the store and bought a shiny new device whose advertising said that it supported USB 2.0 Full Speed?

A device that transferred data at the old USB 1.x "up to 12 Mbps" speed! To get "up to 480 Mbps" speeds, you had to know to look for the magic words "USB 2.0 High Speed."

betaneptune wrote:

I don't think they had a Thunderbolt version. Would have been even more expensive, no?

Of course.

One drive I have mentions (on the box) USB 3.2 Gen 1, which is specific enough to narrow it down to one version!

Remember that it is always "up to". There are many factors that can influence the speed across the shared USB bus. Just because some device compiles with a given version of a given protocol doesn't mean it is going to reach any particular speed.

The nice thing about Thunderbolt is that it is closer to then main system bus. When you connect a Thunderbolt drive, it is only external in physical location. Thunderbolt storage is almost indistinguishable from internal storage.