SD Card Backup Keeps Disconnecting? Lessons From Copying 6,728 Wedding Photos
On September 19 I sat down to move 6,728 wedding photos from memory cards to my computer. There were two cards, so I did what most people would do to save time: I plugged two card readers of the same model into the PC, one card in each, and started both copies at once.
Every two to four minutes, both copies stopped together. An error popped up, the cards vanished from the computer for a moment, then came back. Over and over.
Wedding photos cannot be reshot. Speed mattered much less than making sure every single file arrived. By the end of the day I had learned three things: why two readers running together kept dropping out, what to copy with when the connection is unreliable, and why my first explanation for a strange speed difference was wrong. If you shoot events and come home with several full cards, you may run into the same problems, so here is what happened and what I would check.
1. Two readers, one hidden path
My first suspect was the USB port. I moved the readers between two ports on the back of the case and the USB-C port on the front. I swapped cables. I shut down a background program that frees up memory. None of it made any difference.
Then I unplugged one of the readers. The dropouts stopped immediately. While the remaining reader copied its card, there was not a single error.
The answer was inside the computer. The front USB-C port and the rear ports all sat behind the same root hub. From the outside I was using different sockets, but on the inside both readers were sharing one path. I did not pin down exactly what that shared path was running short of. What I did confirm is simple: with both readers on the same path, both dropped out; with one reader on it, nothing dropped.
If you are on Windows, here is how to see this for yourself.
With several cards, the simplest fix is to copy them one at a time. If you really want to run two at once, first check that the two readers are on different root hubs.
2. Why I stopped dragging files in File Explorer
While the cards kept dropping, copying by drag and drop in File Explorer made things worse. Every time a card disappeared, an Item Not Found window opened and the copy froze until someone clicked Try Again or Skip. If you step away, it just sits there waiting. If you click Skip, nothing records which file you skipped. Out of several thousand photos, there is no way to know afterwards how many never made it.
So I switched to robocopy, a copy command that comes built into Windows. You type it into Command Prompt or a PowerShell window like this:
robocopy "card folder" "destination folder" /E /R:5 /W:2
Instead of opening a window and waiting for you, robocopy retries by itself. If the copy is interrupted and you run the same command again, it skips the files that are already there and carries on with the rest. When it finishes, it prints a summary with how many files were copied, skipped, mismatched and failed. That day it finished with zero failed and zero mismatched.
3. A 4x speed gap that was not the cable
Once I was using one reader at a time, I noticed something else. One card read at 38.8 MB per second. The other read at 154.6 MB per second. Almost four times faster.
38.8 MB/s is about the ceiling you see when a device is connected at USB 2.0 speed. The AI assistant I was troubleshooting with pointed at the cable. Some USB-C cables sold for charging only carry data at USB 2.0 speed, so a charging cable on the slow reader would explain the number neatly.
Then I tested it, and the cable was not it. I swapped the two cables between the readers. I replaced both with new USB-A cables and plugged them into the back of the case. The slow side stayed slow. The new readings were 28.7 MB/s and 102 MB/s. The slow speed did not follow the cable. It followed the combination of card and reader.
File size was not the reason either. Photos on the slow card averaged 21.9 MB each, 1.7 times larger than the 13.3 MB average on the fast card. Larger files usually copy faster per megabyte, because the fixed overhead for each file matters less. Yet the slow card was 3.5 times slower.
The most likely explanation is the link speed itself. In Device Manager, the fast reader sat below a Generic SuperSpeed USB Hub, which confirms it was connected at USB 3 speed. The slow reader was attached directly to the root hub, so I could not see what speed it had negotiated. That is why I am not calling the cause settled. The way to settle it is to swap the two cards between the readers. If the slow speed follows the card, it is the card. If it stays with the reader, it is the reader or its connection.
The first conclusion went wrong for an ordinary reason. Between the two measurements, both the card and the cable had changed, and the whole difference got pinned on the cable. When you change two things at once, you cannot say which one mattered. Change one thing, measure, then change the next.
Three checks before a card gets wiped
A message saying the copy is complete does not prove everything arrived. After the copy, I checked the result three separate ways.
Until all three match, the card does not get formatted. That is the rule worth keeping no matter what tool you copy with.
The short version
If you are a couple wondering when and how you would receive the full set of originals from a ceremony shoot, I have laid out the whole timeline in Korean wedding photography, from booking to delivery. If you are planning to bring your own camera to the studio for a self-shoot, the day-of plan is in a two-hour plan for a rental studio self-portrait session.
Booking information
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