readynas 2304 seems to be timing out

having some weird issues with a few of these units all of a sudden, they're used as video storage for our camera systems with iscsi.  the pc never drops pings to the devices, we're getting iscsi timeouts, top shows very low cpu usage around 5%, but the GUI fails to respond alot, and windows keeps generating iscsi comm errors event 27 an 9 as mentioned.  the storage on the devices is max'd out which causes me to receive saying less than 10% of your storage is available, etc, etc.  however i dont see a slow down per top, unless it is occuring on the disk sub system of which i seem unable to view top stats about.  can anyone point me in a direction here of what could be causing the issue?