|
Most of the 2GB products will have the ability to run at 1GB speeds also. However, there are some areas where this could be interesting in product implementations.
Existing 1GB products are not made to work at 2GB nor to negotiate their speeds. So it's entirely up to the 2GB product to make everything work - but can it? For example, consider a 2GB HBA connecting through a 2GB switch to a 2GB disk subsystem.
Now let's tweak this scenario and say the HBA needs to communicate to a tape library running at 1GB through a different port on the same switch. What happens then? Does the switch buffer up more data and act as a speed matching service? If so, how many of these speed-matching services can it provide? Should speed differences change flow control credits - it could make sense? Maybe the HBA will have to throttle itself down to 1GB? If so, will the switch port understand what the HBA is doing? Because SANs are somewhat dynamic, it is challenging to understand how "new" 1GB products introduced into a SAN with 2GB products will work without creating problems at some level. There is a lot to coordinate among HBAs, switches, hubs, bridges and storage subsystems. The history of the FC industry has not been paved with smooth compatibility. One can only imagine that speed differences could be another area of "disagreement" in implementations.
I'd love to hear from people who have worked on the FC 2GB standard about this. As it is with most things, the intention of the standard and the implementation of products are sometimes different.
Great question, Brian, sorry I can't be a soothsayer and tell you how it will be. Hopefully readers will get something from this that will help them start thinking about their own implementation issues.
|
