I just checked again. It does the same thing when doing render and replace (transcoding) of a AE dynamic link too. It shows disk usage at 100% and network under minor periodic useage. I tried tranferring a file from the server, and the network useage does show 100% during the transfer.
Also i checked resource monitor, and according to it, after effects, (the program handling the transcoding), even though it is only writing 50 mb/s to my drive which can do 1500 mb/s it says its using 100% disk, and its and reading almost nothing.