How Virtual Machines Access Storage and How to View via Virtual Center Server

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 the ESX Server system uses to connect to a storage device. ESX Server supports Fibre Channel (FC), Internet SCSI (iSCSI), and NFS protocols.

The diagram here depicts five virtual machines using different types of storage to illustrate the differences between each type.

 

Viewing Storage Information in the Virtual Infrastructure Client

1)     Displaying Datastores

Datastores are added to the VI Client in one of two ways:

	Discovered when a host is added to the inventory – When you add a host to the inventory, the VI Client displays any datastores recognized by the host.
	Created on an available storage device – You can use the Add Storage option to create and configure a new datastore..

You can view a list of available datastores and analyze their properties.

To display datastores, on the host Configuration tab, click the Storage (SCSI, SAN, and NFS) link.

For each datastore, the Storage section shows summary information, including:

• Target storage device where the datastore is located.
• Type of file system the datastore uses.
• Total capacity, including the used and available space.

To view additional details about the specific datastore, select the datastore from the list. The Details section shows the following information:

• Location of the datastore.
• Individual extents the datastore spans and their capacity.
• Paths used to access the storage device.

You can edit or remove any of the existing datastores. When you edit a datastore, you can change its label, add extents, or modify paths for storage devices

Viewing Storage Adapters

The VI Client displays any storage adapters available to your system.

To display storage adapters, on the host Configuration tab, click the Storage Adapters link.

You can view the following information about the storage adapters:

	Existing storage adapters.
	Type of storage adapter, such as Fibre Channel SCSI or iSCSI.

Details for each adapter, such as the storage device it connects to and target ID.

To view configuration properties for a specific adapter, select the adapter from the Storage Adapters list.

In the diagram, the Fibre Channel storage adapter “vmhba0” is selected. The Details view provides information about the number of LUNs the adapter connects to and the paths are uses.

If you want to change the path’s configuration, you can select this path from the list, right-click the path, and click Manage Paths to bring up the Manage Paths wizard

 

Storage Device Naming

In the VI Client, the name of a storage device is displayed as a sequence of three or four numbers, separated by colons, such as vmhba1:1:3:1. The name has the following meaning:

<HBA>:<SCSI target>:<SCSI LUN>:<disk partition>

The abbreviation vmhba refers to different physical HBAs on the ESX Server system. It can also refer to the virtual iSCSI initiator that ESX Server implements using the VMkernel network stack. The forth number indicates a partition on a disk or LUN. When a datastore occupies the entire disk or LUN, the forth number isn’t present.

The vmhba1:1:3:1 example refers to the first partition on SCSI LUN3, SCSI target 1, which is accessed through HBA 1.

While the third and the forth numbers never change, the first two numbers can change.

For example, after rebooting the ESX Server system, vmhba1:1:3:1 can change to vmhba3:2:3:1, however, the name still refers to the same physical device. The first and the second numbers can change for the following reasons:

• The first number, the HBA, changes when an outage on the Fibre Channel or iSCSI network occurs. In this case, the ESX Server system has to use a different HBA to access the storage device.
• The second number, the SCSI target, changes in case of any modifications in the mappings of the Fibre Channel or iSCSI targets visible to the ESX Server host.