Wblankenship

I just bought an External USB hard drive backup system for my small company. It works just like they said it would. I plugged it in and the OS recognized the five drives as if they were installed in the local machine. The problem is, when I pull the drives to take off site on Friday and throw next weeks drive in all my drives get new letters. This is causing me to have to redo my backup schedule for the new drive letters. Anyone have any suggestions on what to do?