Answer: They are vMotion, HA & DRS! Though all of these 3 features are similar in nature, and are likely to have a common code-base, the implementation (customer's use cases) are different. The differences being:
- vMotion is the user initiated live migration of a guest VM across hosts (ESXServers). The guest OS is hot (running) and will be moved to a new host with the most minimal delay. The network & storage connectivity are not lost during this process. The requirements for this to happen are to have a shared storage (NAS, iSCSI or FC) among the two ESXServers where the guest OS resides and access data + common CPU architectures on the hosts. Both hosts need to be on the same virtual center too.
- HA involves load balancing of the physical systems to maximize the usage of guest OS instances. If there is higher load, the guest OSes would be distributed uniformly across servers. Conversely, if one or more the ESXServers are under-utilized they would also go to power down mode
- DRS involves kick-starting guest OS instances on another ESXserver in case of server crashes or hardware issues on ESXServer
