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December 10th, 2022 06:00
U3223QE, USB-C downstream performance is poor
I have two U3223QE monitors connected to each other. The connection is like this:
Dell Latitude 7480 USB-C <--> U3223QE monitor #1 <---> U3223QE monitor #2
Where monitor #1 is connected to monitor #2 using USB-C Multi-Stream Transport.
I have noticed that when I plug in an external SSD (e.g. SanDisk Extreme Portable SSD) into the downstream USB-C port on these monitors (e.g. the USB-C port on the bottom edge of the monitor) I get horrible USB-C performance.
Using 'winstat' I get:
> Disk Random 16.0 Read 29.56 MB/s 6.2
> Disk Sequential 64.0 Read 34.50 MB/s 4.6
> Disk Sequential 64.0 Write 32.26 MB/s 4.5
In another test I unplugged my laptop from my monitors to free up the laptops only USB-C port. I then plugged the SSD directly into the laptop (bypassing the monitors) and I got MUCH better performance.
> Disk Random 16.0 Read 340.67 MB/s 8.1
> Disk Sequential 64.0 Read 732.95 MB/s 8.3
> Disk Sequential 64.0 Write 785.03 MB/s 8.3
Is this huge difference in performance due to the USB-C interface being saturated when I'm using my laptops only USB-C port to provide downstream connectivity (e.g. drive two monitors, network connectivity through the monitors RJ-45 port, downstream USB peripherals)?
Is there a solution for this issue, other than perhaps buying a laptop / PC that has more than one USB-C port on it?
Thank you!
DELL-Chris M
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December 10th, 2022 10:00
To drive both U3223QE at 3840x2160, the AC power adapter must be attached to the Latitude 7480 and you must be using our 1M/3.2FT USB-C cables.
On both U3223QE, test the Menu- Display- USB-C Prioritization. There are two options =
High Data Speed
High Resolution
BDub122
3 Posts
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December 11th, 2022 18:00
Hi Chris. I tried your suggestion. I already had the AC adapter plugged into the Latitude 7480, and I was already using the 1M USB-C cables that shipped with my two U3223QE monitors. Indeed, both monitors are running at 3840x2160 resolution.
Both monitors had "USB-C Prioritization" set to "High Resolution". When I set the primary (first) monitor to "High Data Speed" the second (downstream) monitor dropped its resolution from 3480x2160 to 1080x2048 in response, and removed the 3480x2160 option from the list of available resolutions to chose from for that monitor in the Windows Display Settings app. The primary monitor remained at 3480x2160.
My conclusion is that when I choose "High Data Speed" on the primary monitor it can no longer drive the downstream (secondary) monitor at 3480x2160 since I've chosen to prioritize data speed over resolution. Do you agree with this analysis, and is it what you expected would happen?
Separately, can you think of a way that I can run both monitors at 3480x2160 while also obtaining high data speeds for a USB-C connected SSD?
My guess is that I'm exhausting the bandwidth that the single USB-C port on the Latitude 7480 can provide, and I would need to purchase a laptop with more than one USB-C port to accomplish what I'm trying to do. However, a quick Google search reports that "USB Type C connectors support 10 Gbps of data transfer through each of two data pin pairs". I think that means up to 20 Gbps for a single USB-C port.
BDub122
3 Posts
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December 20th, 2022 11:00
Hi Chris. I tried your suggestion. I already had the AC adapter plugged into the Latitude 7480, and I was already using the 1M USB-C cables that shipped with my two U3223QE monitors. Indeed, both monitors are running at 2840x2160 resolution.
Both monitors had "USB-C Prioritization" set to "High Resolution". When I set the primary (first) monitor to "High Data Speed" the second (downstream) monitor dropped its resolution from 3480x2160 to 1080x2048 in response, and removed the 3480x2160 option from the list of available resolutions to chose from for that monitor in the Windows Display Settings app. The primary monitor remained at 3480x2160.
My conclusion is that when I choose "High Data Speed" on the primary monitor it can no longer drive the downstream (secondary) monitor at 3480x2160 since I've chosen to prioritize data speed over resolution. Do you agree with this analysis, and is it what you expected would happen?
Separately, can you think of a way that I can run both monitors at 3480x2160 while also obtaining high data speeds for a USB-C connected SSD?
My guess is that I'm exhausting the bandwidth that the single USB-C port on the Latitude 7480 can provide, and I would need to purchase a laptop with more than one USB-C port to accomplish what I'm trying to do. However, a quick Google search reports that "USB Type C connectors support 10 Gbps of data transfer through each of two data pin pairs". I think that means up to 20 Gbps for a single USB-C port.
DELL-Chris M
Community Manager
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December 20th, 2022 12:00
Do you agree with this analysis, and is it what you expected would happen?
* Correct.
and I would need to purchase a laptop with more than one USB-C port to accomplish what I'm trying to do.
* Before purchasing anything, consider not using the monitor daisy chain and instead use a USB-C dock. Go to the Latitude board and start a new thread.
Thread title = Latitude 7480, two U3223QE, possible USB-C dock?
Explain your current usage model and its restrictions. Let's see if other Latitude 7480 user can offer their thoughts.