I have 2 external Western Digital My Book USB hard drives. I use them for large (to me) backups via NTBACKUP. Completed backup file sizes typically are around 100GB. With drive "BackupX", I only seem to get a throughput of ~60mbps, but with the other drive, "BackupY", I consistently get 4 times that performance at ~240mbps. The slow performing drive/connection (dont know which it is yet) is causing my backups to wrong unreasonably long, often in excess of 6 hours. For essentially hard drive file copies, of course this is crazy talk & should be getting much better performance.
I've verified that both BackupX and BackupY are using USB 2.0 ports, and have swapped out the USB cables too to eliminate that from the mix...no differences though.
I used Advanced USB Port Monitor (great tool) to gather my performance data, but I cannot see what might be the difference between what otherwise appear as identical drives.