If the eSATA drive is connecting via USB it won't show up in the BIOS. I'm not 100% sure, but I think with this setup it is treated as a removable drive and so won't be seen until the relevant drivers are loaded by the operating system. As far as I know the only way to make eSATA drives visible in the BIOS is to connect them using an eSATA backplate connected to a spare SATA port on the motherboard, and that would normally only be necessary if you need the drive to be visible from boot, i.e. if you are using it to hold the operating system.