In reply to J Metz.

J,

Okay. That helps. I must confess, some of the phrasing you chose in the write up could have lead a reader to certain conclusions not based on the facts which is the reason for my asking these questions to clarify what you were saying.

I humbly submit that at its heart the story you are telling is about how Ethernet networks need to be like a FC SAN fabric if you are going to use them to transport block storage traffic for lots of applications. I agree with that observation and have for several years.

But, the devil is in the implementation details, as always seems to be the case. And the detail that needs close attention is the relationship between a "fault domain" and availability of its resources. I believe block storage traffic requires a design that survives complete loss of the fault domain so the application never new about the failure. Or else one day it sucks to be you and your company too.

To be clear, the best practices and design principles validated with FC SANs for a decade and a half are imposed by the requirements of the application (SCSI or FICON)that use the fabric. Therefore the fabric has to be designed to satisfy the application requirements and not the other way around.

Block storage traffic for any application, let alone a 1,000 applications using the same network, requires "guaranteed" delivery even when (not if) a fault domain fails. Thus, A/B fabrics are physically isolated fault domains and they exist to fulfill that guarantee. Short of magic, there isn't any other way to meet the guarantee when faced with real world "details" about what can go wrong.

Why I raise this point is that you can't have your cake and eat it to. If you have to survive complete loss of a failure domain, then you can't share it's resources with any other domain, period. That's the "devilish detail" that converged network architectures never seem to address head on. In fact the price you pay for guaranteed delivery of traffic is that when a failure domains is lost all of its resources are too; there is no "sharing" or you only have one failure domain and now you are lost when disaster strikes.

Thank you for posting this material. It's beneficial.

Best.
Brook.

I didn't say you can't have shared resources and survive some failures. But I did say you can't guarantee survival and have shared resources because that requires magic.