the prerequisite of two-node cluster hot backup with USG firewall:
1 now two-node cluster hot backup only support two equipment to do backup，namely a VRRP set can only contain two USG firewall
2 for two-node cluster hot backup ，we suggest that，both of the configuration files of primary/secondary are should be primary files. Or else，two equipment configure conflict will result in that，after primary/secondary switch bring some problems
3 for two-node cluster hot backup ，require system vision of primary/secondary USG are must all the same. Or else， the configure command and dialog frame are probably different in different version，thereby，cause in mistake turn up in primary/secondary USG configure command and state.
4 for two-node cluster hot backup，require the location，type and amount of interface are all the same，Or else，primary USG backup information is not compatible with the physical configure of secondary USG， cause in mistake turn up in primary/secondary USG swich.
Suggestions and Summary.