How to check USB transfer consistency after an update

Your USB drive or memory card seems slower after an update, or its transfer speed changes each time you test it. A single result can be misleading: the port, card reader, background activity, and available space can all affect the number.

Use the same setup for a few short comparisons. The USB & SD Speed Test measures real read and write speeds, so you can check whether the change repeats instead of relying on one file copy.

Compare transfer speeds consistently

1. Open the USB & SD Speed Test and select the USB drive or memory card you want to check. Make sure you select the removable device, not your computer's internal storage.
2. Use the same computer, port, cable, card reader, and media you used before the update. Connect the device directly rather than through a hub, if possible.
3. Run the read and write speed test. Note both results in MB/s, which means megabytes per second. Read speed and write speed are different measurements, so compare each with its own earlier result.
4. Run the test two more times under the same conditions. Compare the general range, not just the fastest or slowest number. Stop if the device disconnects, reports errors, or becomes unusually hot.

A write test writes data to the selected media. Back up important files first, and don't remove the drive while a test is running. For a broader guide to the speed figures, see how to test a USB flash drive's real speed.

What the results mean

All runs are close to the old result

The update probably did not cause a repeatable transfer slowdown. A small difference is normal: other tasks, storage space, temperature, and the timing of a run can shift the result. If normal file copies still feel slower, check whether the files or the app transferring them changed too.

Every run is slower than before

A repeatable change suggests something about the current connection or system is different. It does not prove the drive is damaged or that the update is at fault. Check the port, reader, cable, and driver before deciding the media itself has slowed down.

Results vary widely between runs

Inconsistent speeds can come from background work, caching, the drive's temperature, or other devices sharing a hub. Close file transfers and backup jobs, wait a few minutes, and repeat the comparison. A few similar results are more useful than one unusually high reading.

Read speed is steady but write speed drops

The device can still return data at a similar rate, while saving data is slower. Write speed often varies more, especially when a drive is nearly full or has to reorganize stored data. Check free space and repeat the test after the device cools.

The drive disconnects or the test fails

This is more than a low speed result. Stop testing and check the connection before trying again. A failing cable, reader, port, or drive can interrupt transfers, and repeated write tests are not a safe way to recover files.

How to narrow down a slowdown

1. Restart the computer. An update may leave a driver or background process waiting for a restart. Restart once, reconnect the device, and compare again.
2. Try a different direct port. Avoid a hub or dock for the comparison. If the speed changes with the port, the connection path is more likely involved than the drive itself.
3. Check the cable or card reader. Try a known-good cable or reader with the same device. For USB-C storage, connector shape alone does not guarantee a particular data speed. See why USB cable quality changes external storage results.
4. Close other storage activity. Pause file copies, cloud sync, backups, and downloads that use the same drive. Wait for activity lights to settle before testing.
5. Check what changed in the update. On Windows 11, open Settings › Windows Update › Update history and review recent driver updates. On macOS, open System Settings › General › Software Update to review available updates. If the slowdown began immediately after a device driver update, use the manufacturer's support instructions before changing or rolling back a driver.
6. Check the media on another computer. Keep the same reader and cable if you can. If the slowdown follows the drive across computers, back up its files and consider replacing it. If it happens only on one computer, focus on that computer's port, adapter, or driver.

When the drive or card may be failing

Low speed alone is not proof of a fault. Treat repeated disconnects, read errors, files that disappear, or a test that stops unexpectedly as warning signs. Copy important data to another device while the drive is still readable, then verify the copied files. Don't keep running write tests on media that is losing data.

If the same symptoms follow the drive to another computer and a different connection, replace it or contact the manufacturer about warranty service. For important data that is no longer readable, stop using the device and seek data recovery advice rather than formatting it.

Why real transfers may not match the test

The speed test gives a useful comparison, but it is not a promise that every file copy will run at the same rate. Large files transfer differently from thousands of small files. The operating system may also cache data, meaning it temporarily holds recent information in memory, and a nearly full drive can write more slowly.

For a fair before-and-after check, use the same device and connection, compare read with read and write with write, and look for a repeated change across a few runs. Avoid testing during an update or while files are being copied.