Tuesday, 22 May 2007

Thin Provisioning - Cisco Style

There have been so many discussions on thin provisioning since the Hitachi USP-V announcement. When a major player takes on a specific technology, all of a sudden we realise that everyone else has already been doing it. Tony Asaro's post probably provides the best summary of those who do it today.

One vendor not appearing on the list is Cisco. Not surprising as they don't produce storage systems, however they do produce fibre channel switches which also implement thin provisioning.

I talked about the issue not that long ago here. Now I'm laying out ports for real and its not as clear as it seems. The low down is if you put ports in "dedicated" mode, you get the port speed reserved (or 4Gbps if you set to auto, regardless of the speed negotiated) and in "shared" mode you have a minimum requirement, 4Gbps ports need 0.8Gbps reserved for instance, and the figure reduces in proportion for 2 and 1Gbps ports. More details can be found here. This means not all combinations are possible and you get "Bandwidth Not Available" messages when you don't expect it. As this was confusing me, I've put together a port speed calculator, you can pick it up at Cisco Rate Calculator.

1 comment:

Marc Farley said...

Chris, Oversubscribing ports on a switch is not at all the same thing as thin provisioning. I guess they share some conceptual characteristics, but I don't think we want to start confusing those two different technologies.