The read speed of a SD card decreases when there is just one card remaining to be read.
The read speed of a SD card decreases when there is just one card remaining to be read.
I capture events using several cameras and devices that rely on 250GB SD cards for storage. All cards operate above 95MB/s, which is the slowest, while the fastest reaches 200MB/s. The system can only identify three readers simultaneously. I am using Windows 10 Home and Pro, as well as Windows 11 Home and Pro, across two different computers.
The situation unfolds this way: I insert three SD cards into the readers and begin transferring them to a 16TB storage drive. Each card reads above 60MB/s (totaling 180MB/s), which matches the destination drive's speed. Once one card is done, the remaining two operate at up to 90MB/s each. This works as expected... until another card finishes. When a single card completes, the read speed plummets to 30MB/s, regardless of which card remains. Some cards read normally, but others consistently hit 30MB/s.
It appears there is a software problem. I have tested various readers and still encounter the same issue. Recently, I upgraded to a new computer and the results remain consistent across both systems—one running Windows 10 Pro and the other Windows 11 Pro. Even when only one SD card is inserted, it starts at 30MB/s but accelerates to 90MB/s once more cards are added, then drops to 60MB/s when the third card begins. The problem only occurs when a single card is active.
I suspect a setting prioritizes multiple readers over others, giving higher priority to one while lowering the priority of the rest—possibly for better performance or data handling. It seems counterintuitive, as all three cards should be processing at once. Any solution would be greatly appreciated.
I use file explorer and have confirmed that the transfer speed indeed drops to 30MB/s with task manager. It’s quite clear you can measure it using a clock. The files from each camera only take a few MB and typically handle 60GB or more. 4K video for 1.5 to 2 hours on 5 cameras. I’m not particularly interested in searching for third-party solutions since there are many mixed with numerous scams. I’ve been down this path more often than I’d like and learned from those mistakes. Many people face the same issue, but no one has found a clear reason or a reliable fix.
My new computer performed well initially but then started behaving similarly. Both my systems are AMD Ryzen 7 2700 eight-core 3.2GHz with 32GB RAM. The only limitation is the 16TB Elements USB drive. When accessing internal SATA SSDs, speeds are much faster except during single-file transfers. It seems something in the software is restricting performance beyond physical limits.
For context, I’ve assembled high-end computers for clients and spent about 30 years in industrial robotics. I don’t have time to troubleshoot Windows issues when they’re not being addressed. I prefer letting those who enjoy the challenge attempt it.
I plan to experiment with a new approach after hearing about Microsoft's USB endpoint restrictions. I purchased six SD dual readers that fit into a 7-port hub, reducing the total endpoints by more than half. Previously, I used UGreen 4-port readers, each reading only one SD card type but opening multiple ports for different cards. With three UGreen readers I gain access to 12 ports, and adding an Elements USB drive, printers, mouse, and keyboard brings the total to 17 endpoints—potentially surpassing the claimed limit of 10 users. Although this might not directly affect this setup, I want the flexibility to insert all five SD cards and complete the transfer without interruption. For some reason, connecting four or more devices disables recognition, showing only three at a time even though they appear in the tree.
Examine the situation as you progress through the cards.
Check Task Manager, Resource Monitor, Performance Monitor, and Process Explorer (Microsoft, free) to track system behavior.
All these are Microsoft tools, not third-party.
Utilize each tool individually but keep only one open at a time.
Keep the window open and observe what occurs.
You should be able to identify when downloads start to slow down.
Task Manager and Resource Monitor make solid first steps.
Process Explorer: https://learn.microsoft.com/en-us/sysint...s-explorer
Performance Monitor demands more time and effort—consider other options first.
The Windows file explorer that comes with Windows remains largely unchanged. One computer uses Windows 10, another uses Windows 11, both upgraded to Pro for group policy features. The file explorer looks similar. My laptop, also running the same AMD Ryzen 7 CPU, has a newer version for laptops that seems aimed at younger users. It receives an "F" rating across all categories. I don’t use it much for file management, though it has nice colors. I’m still figuring out if it does anything useful. Maybe we’re all just starting over again.
I've been dealing with this for years, which is why I think it's a built-in limit unrelated to simply speeding up file transfers. It would be great if Microsoft could focus on fixing the core issue instead of just explaining basic functions. Having worked in college for over 40 years and even teaching basic computer skills, let's concentrate on why two SD cards upload at 90MB/s but drop to 30MB/s once one finishes. I spend some time renaming files on the SD cards before uploading each one, which causes delays because only three can be processed at a time. This results in the last card taking up to 30MB/s for several minutes. Using another SD card restores speeds to 90MB/s or 180MB/s overall. If I could just adjust this process and stop the fake load when the last card is done, it would save a lot of time. Band-aids on broken bones...
It seems the issue is mainly related to the last SD becoming slow—correct? There are no obvious connections to any specific SD card, reader, cables, or USB ports. I believe Process Explorer could be useful. Observe what changes occur during uploads and insertions of SD cards.