I only know vmware in disaster recovery and fault tolerance. If in vmware:
That SRM disaster recovery software, refers to the two cities, such as a data center in Shanghai, a data center in Beijing, when Beijing data center collapsed, Shanghai data center will immediately took up, including storage, servers, and so on up to take over.
Fault tolerance that is vsphere this software in the FT function refers to two different physical servers, server A has a virtual machine is the master, the server B in a virtual machine is backed up, these two virtual machines remain in sync.
When A virtual machine fails broken, then B is the backup virtual machine immediately took up the whole process without any interruption, are connected seamlessly.