San Disk Slim Fit USB 3.2 Gen 1 - very slow performance

I’m using a San Disk Slim Fit USB 3.2 Gen 1 (SanDisk Ultra Fit USB 3.2 Flash Drive | Western Digital) with an Apple MacBook Air 2020. I’m using an Apple USB-A to USB-C dongle. The USB drive is formatted APFS (encrypted). The performance when copying a large file to the drive varies from 1MB/sec to 20MB/sec. There are burst of about 20MB/sec followed by equally long lulls of 1MB/second.

Does anyone have any thoughts on the cause? Is the APFS encryption overhead reducing performance? CPU utilisation is very low. I would have expected much better performance.

Hi @Paul74 ,

Have you opened a Support Case? If not opened, for more information, please contact the SD Technical Support team for best assistance and troubleshooting: