iSCSI, but server is slow

First of all i´m a newbie to iSCSI and Mulitpath, but i think i have
configured the iSCSI initiator and the target (MSA1510i) correctly, because i
have connected targets and i can copy files to and from the targets.

But when i try to do something on my server, the monitor freezes sometimes a
minute or more. The Server is a Dl380 G5 with 14 GB RAM and two 146 GB SAS
with two NIC´s (one connected to the enterprise LAN, one connected to the
ISCSI SAN). After that has happened i can work a few minutes, then getting
the same freeze. Really bad is working if i am connected via RDP.

Does any have any suggestions to this problem?