Although storage systems manage all aspects of virtual volumes, ESXi hosts have no direct access to virtual volumes on the storage side. Instead, ESXi hosts use a logical I/O proxy, called the protocol endpoint, to communicate with virtual volumes and virtual disk files that virtual volumes encapsulate. ESXi uses protocol endpoints to establish a data path on demand from virtual machines to their respective virtual volumes.
Each virtual volume is bound to a specific protocol endpoint. When a virtual machine on the host performs an I/O operation, the protocol endpoint directs the I/O to the appropriate virtual volume. Typically, a storage system requires a very small number of protocol endpoints. A single protocol endpoint can connect to hundreds or thousands of virtual volumes.
On the storage side, a storage administrator configures protocol endpoints, one or several per storage container. Protocol endpoints are a part of the physical storage fabric and are exported, along with associated storage containers, by the storage system through a storage provider. After you map a storage container to a virtual datastore, protocol endpoints are discovered by ESXi and become visible in the vSphere Web Client. Protocol endpoints can also be discovered during a storage rescan.
In the vSphere Web Client, the list of available protocol endpoints looks similar to the host storage devices list. Different storage transports can be used to expose protocol endpoints to ESXi. When the SCSI-based transport is used, the protocol endpoint represents a proxy LUN defined by a T10-based LUN WWN. For the NFS protocol, the protocol endpoint is a mount point, such as IP address and a share name. You can configure multipathing on a SCSI based protocol endpoint, but not on an NFS based protocol endpoint. However, no matter which protocol you use, a storage array can provide multiple protocol endpoints for availability purposes.