VMWare ESXi 4 host server configuration can be backed up to a configuration file using the vSphere CLI which can be downloaded from here: http://www.vmware.com/support/developer/vcli/
The vicfg-cfgbackup.pl script allows you to take a backup of the ESXi Host configuration, components such as networking, storage, IP, DNS and other settings are saved. In a disaster situation we can simply build a new ESXi host and restore the configuration with this script.
E:Program Files (x86)VMwareVMware vSphere CLIbin>vicfg-cfgbackup.pl -save -server 10.10.100.24 -username root -password ******** svm001.bak
E:Program Files (x86)VMwareVMware vSphere CLIbin>vicfg-cfgbackup.pl -load -server 10.10.100.24 -username root -password ******** svm001.bak
You can also do this with the vMA appliance http://www.vmware.com/support/developer/vima/