IRF Between 2 datacenters using 5500s

[sundoo1]

Hi,

I'm new to IRF and I have a question.

One of our clients' network is deployed over 3 distant sites: 2 datacenters and 1 user site.

Now the network is being completely rebuilt. We decided to use 2x 5500s as network cores on each site (6 in total) and interconnect those datacenters in a ring (datacenter1 --> datacenter2 --> Users Site --> datacenter 1)

We decided to use IRF for ease of administration.

Now the questions :

- Is it possible to have 2 IRF domains in total (as in figure attached - irf.jpg - a) ? This would allow using the 2 links (UsersSite Datacenter1 and UsersSite - Datacenter2) in load balancing mode

or

- Will it be better to have 3 IRF domains (as in figure attached irf.jpg - b) - one on each site and to use the links as following:

        - UsersSite Datacenter1 - Active

        - UsersSite - Datacenter2 - Passive

What are the advantages and disadvantages of the 2 connection modes ? What are the risks of the first connection mode ?

Thanks in advance

(see picture attached)