[Dovecot] Fault tolerant architecture

Hi, I'm new to this list and want your help. I'm the mail admin for some domains in Rio de Janeiro - Brazil. Today we have only one machine running dovecot (imap+pop3) with local mail. We are migrating to two virtual machines in kvm running in separate hosts. Then we have two main problems:

• How to share mail files to both dovecots? We've been thinking about NFS using local indexes. Is this a good approach?
• How do we have a fault tolerant mail servers? Our first solutions is using two IP addresses in our DNS records.

About NFS using local indexes, I'm configuring a test server. But how to configure local indexes when my mail_location comes from sql (userdb_home actually). I'm using dovecot 1.2.9.

I guess you already had some of these problems or maybe in another architecture these neither exists.

Thanks for any help,

Marcelo