I had the same problem, needed to backup 200+ GB to a USB HD due to a hardware upgrade. Then I remembered the board had a strange bios reset recently (hence the upgrade) so I checked and set the bios SATA configuration back from IDE to AHCI (My mobo has 3 possible settings IDE, RAID and AHCI). Now it's supper silent (no more swapping to disk) and a steady transfer rate (+/- 27 MB/sec).
This is the solution that helped me, and hopefully some others.
I had the same problem, needed to backup 200+ GB to a USB HD due to a hardware upgrade. Then I remembered the board had a strange bios reset recently (hence the upgrade) so I checked and set the bios SATA configuration back from IDE to AHCI (My mobo has 3 possible settings IDE, RAID and AHCI). Now it's supper silent (no more swapping to disk) and a steady transfer rate (+/- 27 MB/sec).
This is the solution that helped me, and hopefully some others.