Comments on ipSpace.net: VXLAN runs over UDP – does it matter?

You only need large amounts of buffers for long-di...

2012-01-26T10:59:48.196+01:00

You only need large amounts of buffers for long-distance links to keep the link utilized. For local links you really don't need that many. For end devices you typically allocate 16 buffers. In FC all buffers have the same size (a full frame or 2148 bytes) and you use one up whether you transmit a full-size frame or a smaller frame. Is that really that much? That, in my book, it not overprovisioning.

Especially if you say "overprovisioning" with the same meaning as Greg Ferro seems to like so much: FC switch vendors (and the whole storage industry) are greedy and have been stealing your money over the past 15 years just because they like to, to the point of calling users "idiots" for buying into such "bullshit". And since you linked to his article where he expresses just this position, I thought you might endorse that position.

FC switches have the memory resources they need to provide the reliability they need to provide for the criticality of the applications that run on them. They are not overprovisioned so that FC switch vendors can be rich.

Completely agree. From the end application point o...

2012-01-26T01:17:30.262+01:00

Completely agree. From the end application point of view, VXLAN and transport over UDP are completely transparent. The applications will see only the internal packet (TCP or not) and expect the reliability associated with the internal protocol.

I think Infiniband gets pretty good utilization wi...

2012-01-25T20:28:29.166+01:00

I think Infiniband gets pretty good utilization with small buffers thanks to credit-based flow control. Incast can cause congestion trees, though.

In my simplistic understanding of FC, Class 1 offe...

2012-01-25T14:43:01.153+01:00

In my simplistic understanding of FC, Class 1 offers reliable transport because frames are acknowledged by the final receiver, very similarly to what TCP does in IP world. Am I wrong?

As for "over provisioning", you do need large buffers if you want to have reasonable performance with high-speed flow-controlled links, don't you?

Technically, the Fibre Channel standard defines mu...

2012-01-25T10:40:30.686+01:00

Technically, the Fibre Channel standard defines multiple classes of service to be able to offer different types of transport. Class 1 offers a connection-oriented transport with frame acknowledgement, offering a completely reliable transport. But in the real world nobody implemented such classes of service, and the one used for storage 99,999% of the time is class 3 which is unreliable.

Also, FC does not minimize packet loss by overprovisioning the network. It just uses flow control, it's that simple.