While you may finally be able to achieve fast LAN transfers under Windows Vista, the high speed you managed to have gained may not last. The annoying symptom of moving large files over a LAN in Windows Vista’s is that network performance may simply slow down before the file is fully transferred. The problem was not easy to detect since it was not an issue when transferring smaller-sized files. No need to pull out any more hair, here is the solution.
After systematically shutting down services inside Windows Vista SP1, here is a fix that resolved the issue of a slow down in network performance as you transfer large files. My internet security suite
is was Shaw Secure and it turned out that 1 particular setting was causing network performance to drop during large LAN transfers. In order to achieve maximum network performance and sustain high transfer speeds, Shaw Secure’s real-time antivirus protection had to be disabled. Here is a network bandwidth graph of transferring a large file over the LAN with real-time scanning enabled. See the drop in transfer speed after a while and it just never recovered.
If you run Shaw Secure or another security software and your Windows Vista network speed slows down over time, try disabling your real-time anti-virus scanner to see if it fixes the problem. Of course, if you do decide to disable real-time protection, be sure to schedule frequent scans of your computer to keep yourself protected.