In reply to J Metz.

J, Thanks for the response

A few follow ups:

"Right now you can put iSCSI (traditional, non-lossless) in one VLAN and ethernet traffic in another VLAN on the same 10G link. You do not need PFC, ETS, DCBX, or QCN to do this. The traffic will work just fine."

I think the confusion is in the idea that because you CAN converged traffic does not necessarily mean you SHOULD. I would argue VLANs do nothing to ensure QoS...they only isolate traffic logically. You still have to contend with non-storage traffic for fixed, limited switch resources. Without having a mechanisme such as ETS to control bandwidth and PFC to ensure that the other traffic streams are not the cause of a blocked path, there is no way to guarantee the QoS of the iSCSI stream.

"Moreover, FCoE has a explicit requirement for lossless behavior. It’s written into the standard spec (FC-BB-5). Not so for iSCSI."

I would contend that all storage traffic should be lossless. Without PFC (or even 802.3x flow control), relying on TCP - and its longer timeouts - to provide "guaranteed delivery" via TCP Retransmits, is a performance killer.

"ETS doesn’t define the mechanism by which bandwidth groups are defined or allocated. It just so happens that the way vendors do this is through QoS. "

True...but the ETS standard does set certain behavioral expectations to support inter-device copperation and via DCBx the consistent application of ETS settings.

"PFC is 100% completely independent of ETS/QoS"

Not always true. As you state in the previous quote above, the mechanism to manage ETS and ensure that buffers don't become saturated does involve PFC. ETS directly affects buffer utilization. Many switch vendors use PFC to throttle their upstream senders to ensure that the switch can internally honor the ETS limitations.

Bottom line, is that iSCSI can receive all of the same benefits from ETS, PFC, QCN, and DCBx (assuming the iscsi devices support these standards) as FCoE or RDMAoE. You are correct that iSCSI does not technically require any of these to operate, but the advantages of these standards when attempting to share the network with non-iSCSI traffic is real.

Keep up the great work! I totally enjoy your posts...very informative and thought provoking.