The solution presented in this document is designed to simulate a very large number of mailboxes hosted with VMWare ESXi 5.0 hypervisor on highly redundant hardware with virtual servers. Application level redundancy (Exchange DAG) is augmented with redundant storage to create a highly available and fault tolerant solution.  The Mailbox Resiliency features of Exchange 2010 have greatly enhanced the availability of Exchange 2010, while also improving I/O performance. The solution presented here is a Mailbox Resiliency solution utilizing 2 Database Availability Groups (DAGs) and 2 copies of every database. The tested environment simulates all users in these DAGs running on a single Storage Center of the 2 Storage Center configurations, as in a failover event. The number of users simulated was 50,000 across 12 virtual servers on 6 physical hosts, (6 servers per DAG), with 4,166 users per server (4168 on 4 of 12 servers). The mailbox size was 2GB per user. Each server has 6 databases, with one copy local and the second copy replicated to a second server on a second Storage Center. This provides redundancy through hardware and software.