On Nov 4, 2013, at 11:02 AM, Nicholas A. Bellinger <nab@xxxxxxxxxxxxxxx> wrote: <snip> >> As I understand it FCOE only works over lossless ethernet. Lossless >> ethernet has the ability to send pause and unpause frames and does not >> reorder or loose packets. > > That's not exactly true. It's still completely possible to run FCoE > over normal 1 Gb/sec ports in VN2VN mode (eg: point to point) without > Lossless ethernet. Packet loss is extremely disruptive to FCoE. It is true that DCB is not required - link flow control can be used instead - but the environment for the FCoE traffic really should be lossless. Link flow control has limitations that can result in deadlocks, which is at least one reason DCB was created. You can reduce the likelihood of such deadlocks in a link flow control environment by dedicating an interface to your FCoE traffic with link flow control enabled, and running other traffic through a separate physical link either with or without link flow control on that traffic. >> However in the past lossless ethernet does not >> seem to be standarized and had a few problems: It only works over a >> single layer 2 hop, it does not work cross-vendor (e.g. is not >> standardized), link aggregation does not work because that out of order >> transmissions would be possible which breaks FCOE, lossy traffic gets >> paused by lossless traffic and so one. So I wonder what the current >> state of lossless ethernet is? I saw FCOE in Cisco UCS blades and HP >> Blades but they always use Internet Connect Bays or Top of the Rack >> switches to change it in FC and than go to a FC storage. I wonder if it >> is these days possible to go end-to-end. I noticed that some storage >> arrays like EMC VNX, HP 3PAR, Hitachi HDS and so on support but I never >> seen an environment where it was end-to-end not even over a single layer >> 2 HOP. It should work over a layer 2 hop, but you do need to know how your switches behave with regards to flow control. DCB-enabled switches that permit the use of PFC should do ok here. >> I would appreciate if you or someone else could shed some light into >> the lossless ethernet topic. I'm afraid I am not quite an expert here. I don't know about degrees of interoperability between switches and such. I know enough to worry about it though. I would be very wary of attaching some low-end switch to a high-end switch with any expectation of getting lossless behavior with such a setup. A low-end switch with just link flow control might work in some small environments, however. > Mmm, this would be a type of question for Robert Love + MDR. (CC'ed) We can try. It can get very complicated. If you really need storage access across a network that you cannot make lossless, I would not use FCoE but rather iSCSI. > --nab -- Mark Rustad, Networking Division, Intel Corporation
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