USB 3 device not fully utilized?

[lijsfgfdgdf]

I wonder how to find the bottleneck:

I compare 2 HDD by content. FFS compares at ~ 90 MB/s. Both devices are utilized only 40-50% by FFS according to Windows Task Manager.
If I copy files from any drive to the internal ssd using Windows Explorer, ~ 175MB/s are reached each.
If I copy files from each drive to the internal ssd using Windows Explorer in parallel, ~ 150 MB/s are reached
(non-cached files, first read access after connecting the drive)

If the files would be fragmented, I would expect slow performance, but drive utilisation should be high.
I made sure to try same as well as different USB controllers for each drive.

FreeFileSync_x64.exe has only 1-2% CPU utilisation, so it is not a single-threading limitation of FFS.

So if neither drive a or b nor usb or cpu is the bottleneck, why does FFS not compare at ~ 150 MB/s ?

Thank you.

[xCSxXenon]

How fast does FFS actually transfer?

[lijsfgfdgdf]

Well, most files are not copied because they are identical. The copy speed depends on file size and fragmentation on both ends, of course.
Currently both drives are synced, but I will check the transfer speed the next time.