It may happen that the following warning will appear in the DSS V6 event viewer and in the dmesg logs:
CONFIG_TCP_ZERO_COPY_TRANSFER_COMPLETION_NOTIFICATION not enabled in your kernel.
ISCSI-SCST will be working with not the best performance. Refer README file for details.
But it doesn't mean that your DSS V6 performance is degraded. This warning is being automatically generated by one of the internal modules but the TCP zero copy was disabled on purpose, because it has caused unstable behavior in DSS V6.
We've also made several tests which confirmed that it doesn't have any significant impact on the iSCSI performance.