Each ProxySG model has its own specifications for the number of clients it can handle, bandwidth, and so forth. Because each model differs in their performance specifications, for optimal performance, Blue Coat recommends and supports using the same ProxySG appliance models in a failover environment because when failover occurs, a lower specification ProxySG might not be able to handle the traffic. For example, you would not want to have a ProxySG 510 as a failover for a ProxySG 8100.