A virtual disk hides the physical storage layer from the virtual machine's operating system.

Regardless of the type of storage device that your host uses, the virtual disk always appears to the virtual machine as a mounted SCSI device. As a result, you can run operating systems that are not certified for specific storage equipment, such as SAN, in the virtual machine.

When a virtual machine communicates with its virtual disk stored on a datastore, it issues SCSI commands. Because datastores can exist on various types of physical storage, these commands are encapsulated into other forms, depending on the protocol that the ESXi host uses to connect to a storage device.

Virtual Machines Accessing Different Types of Storage depicts five virtual machines that use different types of storage to illustrate the differences between each type.

Virtual Machines Accessing Different Types of Storage
Displays relations between virtual machines and different types of storage. A group of virtual machines on a single host are connected to storages of type fibre array, iSCSI array, and NAS appliance. The virtual machines connected to iSCSI array and NAS appliance require TCP/IP connectivity. The fibre array and iSCSI array storages are connected to VMFS instances, while the NAS appliance is connected to an NFS instance. Both VMFS and NFS are connected to LAN nodes. The fibre array LAN node is connected to a fibre channel HBA. The firs iSCSI array LAN node is linked to an iSCSI hardware initiator and the second LAN node is connected to a software initiator through an ethernet NIC. The NAS appliance LAN node is connected to an ethernet NIC. An additional virtual machine is linked to VMFS on the host through local ethernet SCSI.

You can use vCLI commands to manage the virtual machine file system and storage devices.

VMFS - Use vmkfstools to create, modify, and manage VMFS virtual disks and raw device mappings. See Managing the Virtual Machine File System with vmkfstools for an introduction and the vSphere Storage documentation for a detailed reference.

Datastores - Several commands allow you to manage datastores and are useful for multiple protocols.

LUNs - Use esxcli storage core or vicfg-scsidevs commands to display available LUNs and mappings for each VMFS volume to its corresponding partition. See Examining LUNs.

Path management - Use esxcli storage core or vicfg-mpath commands to list information about Fibre Channel or iSCSI LUNs and to change a path’s state. See Managing Paths. Use the ESXCLI command to view and modify path policies. See Managing Path Policies.

Rescan - Use esxcli storage core or vicfg-rescan adapter rescan to perform a rescan operation each time you reconfigure your storage setup. See Scanning Storage Adapters.

Storage devices - Several commands manage only specific storage devices.

NFS storage - Use esxcli storage nfs or vicfg-nas to manage NAS storage devices. See Managing NFS/NAS Datastores.

iSCSI storage - Use esxcli iscsi or vicfg-iscsi to manage both hardware and software iSCSI. See Managing iSCSI Storage.

Software-defined storage - vSphere supports several types of software-defined storage.

vSAN storage - Use commands in the esxcli vsan namespace to manage vSAN. See Monitoring and Managing vSAN Storage.

Virtual Flash storage - Use commands in the esxcli storage vflash namespace to manage VMware vSphere Flash Read Cache.

Virtual volumes - Virtual volumes offer a different layer of abstraction than datastores. As a result, finer-grained management is possible. Use commands in the esxcli storage vvol namespace.