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 just a few 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. The protocol endpoints are a part of the physical storage fabric. The storage system exports the protocol endpoints with associated storage containers through the storage provider. After you map the storage container to a Virtual Volumes datastore, the ESXi host discovers the protocol endpoints and they become visible in the vSphere Client. The protocol endpoints can also be discovered during a storage rescan. Multiple hosts can discover and mount the protocol endpoints.
In the vSphere Client, the list of available protocol endpoints looks similar to the host storage devices list. Different storage transports can be used to expose the 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 an IP address and a share name. You can configure multipathing on the SCSI-based protocol endpoint, but not on the NFS-based protocol endpoint. No matter which protocol you use, the storage array can provide multiple protocol endpoints for availability purposes.
Protocol endpoints are managed per array. ESXi and vCenter Server assume that all protocol endpoints reported for an array are associated with all containers on that array. For example, if an array has two containers and three protocol endpoints, ESXi assumes that virtual volumes on both containers can be bound to all three protocol points.