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. The host uses the resulting data, in particular the Page 83 information, to generate a unique identifier. Device identifiers that are based on Page 83 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 website.

Path-based identifier.

When the device does not provide the Page 83 information, the host generates an mpx.path name, where path represents the first 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 not unique or persistent, and can change after every system restart.

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 when 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.

Legacy Identifier

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

vml.number

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

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