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
You can use vCLI commands to
manage the virtual machine file system and storage devices.
- VMFS - Usevmkfstoolsto create, modify, and manage VMFS virtual disks and raw device mappings. See Managing the Virtual Machine File System with vmkfstools for an introduction and thevSphere Storagedocumentation for a detailed reference.
- Datastores - Several commands allow you to manage datastores and are useful for multiple protocols.
- LUNs - Useesxcli storage coreorvicfg-scsidevscommands to display available LUNs and mappings for each VMFS volume to its corresponding partition. See Examining LUNs.
- Path management - Useesxcli storage coreorvicfg-mpathcommands 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 - Useesxcli storage coreorvicfg-rescan adapter rescanto 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 - Useesxcli storage nfsorvicfg-nasto manage NAS storage devices. See Managing NFS/NAS Datastores.
- iSCSI storage - Useesxcli iscsiorvicfg-iscsito manage both hardware and software iSCSI. See Managing iSCSI Storage.
- Software-defined storage - vSphere supports several types of software-defined storage.
- storage - Use commands in theesxcli vsannamespace to manage . See Monitoring and Managing Storage.
- Virtual Flash storage - Use commands in theesxcli storage vflashnamespace 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 theesxcli storage vvolnamespace.