Understanding Storage Device Naming

Each storage device, or LUN, is identified by several names.

Device Identifiers

Depending on the type of storage, the ESXi host uses different algorithms and conventions to generate an identifier for each storage device.

SCSI INQUIRY identifiers.

The host uses the SCSI INQUIRY command to query a storage device and uses the resulting data, in particular information, to generate a unique identifier. Device identifiers that are unique across all hosts, persistent, and have one of the following formats: ■ naa.number ■ t10.number ■ eui.number These formats follow the T10 committee standards. See the SCSI-3 documentation on the T10 committee Web site.

Path-based identifier.

When the device does not provide the Page 83 information, the host generates an mpx.path name, where path represents the path to the device, for example, mpx.vmhba1:C0:T1:L3. This identifier can be used in the same way as the SCSI INQUIRY identifies. The mpx. identifier is created for local devices on the assumption that their path names are unique. However, this identifier is neither unique nor persistent and could change after every boot.

Legacy Identifier

In addition to the SCSI INQUIRY or mpx. identifiers, for each device, ESXi generates an alternative legacy name. The identifier has the following format:

vml.number

The legacy identifier includes a series of digits that are unique to the device and can be derived in part from the Page 83 information, if it is available. For nonlocal devices that do not support Page 83 information, the vml. name is used as the only available unique identifier.

Example: Displaying Device Names in the vSphere CLI

You can use the esxcli --server=server_name storage core device list command to display all device names in the vSphere CLI. The output is similar to the following example:

# esxcli --server=server_name storage core device list
naa.number
 Display Name: DGC Fibre Channel Disk(naa.number)
 ... 
 Other UIDs:vml.number

Runtime Name

In the vSphere Client, you can see the device identifier and a runtime name. The runtime name is generated by the host and represents the name of the first path to the device. It is not a reliable identifier for the device, and is not persistent.

Typically, the path to the device has the following format:

vmhbaAdapter:CChannel:TTarget:LLUN

■	vmhbaAdapter is the name of the storage adapter. The name refers to the physical adapter on the host, not to the SCSI controller used by the virtual machines.
■	CChannel is the storage channel number. Software iSCSI adapters and dependent hardware adapters use the channel number to show multiple paths to the same target.
■	TTarget is the target number. Target numbering is determined by the host and might change if the mappings of targets visible to the host change. Targets that are shared by different hosts might not have the same target number.
■	LLUN is the LUN number that shows the position of the LUN within the target. The LUN number is provided by the storage system. If a target has only one LUN, the LUN number is always zero (0).

For example, vmhba1:C0:T3:L1 represents LUN1 on target 3 accessed through the storage adapter vmhba1 and channel 0.