Introduction to Storage
Fibre Channel SAN arrays, iSCSI SAN arrays, and NAS arrays are widely used storage technologies supported by VMware vSphere to meet different datacenter storage needs. The storage arrays are connected to and shared between groups of servers through storage area networks. This arrangement allows aggregation of the storage resources and provides more flexibility in provisioning them to virtual machines.
vSphere Datacenter Physical Topology
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 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
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.
Datastores
ESXi hosts use storage space on a variety of physical storage systems, including internal and external devices and networked storage. A host can discover storage devices to which it has access and format them as datastores. Each datastore is a special logical container, analogous to a file system on a logical volume, where the host places virtual disk files and other virtual machine files. Datastores hide specifics of each storage product and provide a uniform model for storing virtual machine files.
Depending on the type of storage you use, datastores can be backed by the following file system formats:
Virtual Machine File System (VMFS). High-performance file system optimized for storing virtual machines. Your host can deploy a VMFS datastore on any SCSI-based local or networked storage device, including Fibre Channel and iSCSI SAN equipment.
As an alternative to using the VMFS datastore, your virtual machine can have direct access to raw devices and use a mapping file (RDM) as a proxy. See Managing the Virtual Machine File System with vmkfstools.
Network File System (NFS). File system on a NAS storage device. ESXi supports NFS version 3 over TCP/IP. The host can access a designated NFS volume located on an NFS server, mount the volume, and use it for any storage needs.
Storage Device Naming
Each storage device, or LUN, is identified by several names.
Name. A friendly name that the ESXi host assigns to a device based on the storage type and manufacturer, for example, DGC Fibre Channel Disk. This name is visible in the vSphere Client.
Device UID. A universally unique identifier assigned to a device. The type of storage determines the algorithm used to create the identifier. The identifier is persistent across reboots and is the same for all hosts sharing the device. The format is often naa.xxxxxxx or eui.xxxxxxxx.
VML Name. A legacy SCSI device name specific to VMware. Use the device UID instead.
The runtime name of the first path to the device is a path identifier and not a reliable identifier for the device. Runtime names are created by the host, and are not persistent. The runtime name has the format vmhba#:C#:T#:L#. You can view the runtime name using the vSphere Client.