Hello,
The ESA comes in different form factors. The first is the appliance model which has varying degrees of redundancy built in.
The C170 has software RAID on the hard drives
The C360/C670/X1070 have hardware RAID as well as redundant power supplies installed.
The software comes installed on the hardware as it's an appliance. Your company is licensed based on the # of mailboxes and features desired. You can run any number of appliances with those licenses to cover things such as redundant data centers and the amount of incoming/outgoing mail flows. Your Cisco account team can help you with sizing the solution.
The second is Virtual and you can simply spin up the number of virtual instances to cover your mail flow needs as well as redundancy.
The third form factor is cloud. Your Cisco account team will help you size the cloud solution to fit your needs and the capacity assurance clause of the contract will let your cloud solution grow up to 50% more as needed to handle capacity.
Raymond
