I have seen this error before related to sometimes either with different initiator settings not matching the Target or you need to increase the MaxRecvDataSegmentLength and MaxXmitDataSegmentLength to 65536 under Hardware Tools(ALT+CTRL+W) -> Tuning optons -> iSCSI Daemon options. Also have seen this with bonding issues but since you have had an increase in I/O with changing the WB feature for the Target Volume this would eliminate network related issues.

Thanks for assisting with the LSI selection for Johhny