How Virtual Machines Access Storage

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
host uses to connect to a storage device.
Figure 1 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.
  • Software-defined storage - vSphere supports several types of software-defined storage.
    • storage - Use commands in the
      esxcli vsan
      namespace to manage
      . See Monitoring and Managing 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.