Symptoms
- Copying files takes far longer than expected for the file size
- Transfer speed shown in the copy dialog is much lower than the drive's rated speed
- Speed is fine for small files but crawls with many small files
- Speed dropped noticeably compared to when the drive was new
Likely causes
- CommonDrive or port is USB 2.0 instead of USB 3.0/3.1USB 2.0 tops out around 35–40 MB/s versus hundreds for USB 3.0.
- CommonCopying many small files instead of a few large onesSmall files have more overhead per file, slowing overall transfer rate.
- PossibleMechanical hard drive nearing full capacity or fragmentedBoth increase how much the drive head has to move.
- PossibleDrive formatted with a file system not optimized for the transfer typeSome formats handle large numbers of files less efficiently than others.
- PossibleFailing drive with degraded read/write performanceA drive with developing errors slows down as it retries failed operations.
What to do
- Check that both the port and cable are USB 3.0/3.1 rated, not USB 2.0.
- Compare transfer speed for one large file versus many small files to identify which is slow.
- Check the drive's free space and consider defragmenting if it's a traditional hard drive that's nearly full.
- Try copying to a different, known-fast drive to see if the source or destination is the bottleneck.
- Run a benchmark tool to compare actual speed against the drive's rated specs.
- If speeds are far below rated specs even with a good USB connection, check the drive's health for early failure signs.
Tools and parts
- Benchmark tool
When to call a pro
If a benchmark shows speeds far under the drive's rating and health checks look fine, the drive or its controller may still be worth having tested professionally.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.