ADFS 2.0: cluster or two standalone servers

I'm wondering if it is necessary to use SQL cluster mirroring for ADFS site resiliency and failover.

1. I have 2 sites, connected by a site-to-site VPN
2. I use an external host for DNS. It points to the main site but is configured to failover the ADFS server's A record to point to the other site's IP in the event the main site is unreachable (and failback the A record when connectivity is restored).
3. I'd like to put 1 federation server in each site each configured identically to each other (same relying party trusts, communication, decrypting, signing certs), each server uses its own local database (WID or SQL). Any configuration changes going forward would of course have to be performed on each server but that is ok.

Is this possible? Thanks for any feedback.