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

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SCSI INQUIRY identifiers - The host uses the SCSI INQUIRY command to query a storage device and uses the resulting data, in particular the Page 83 information, to generate a unique identifier. SCSI INQUIRY device identifiers are unique across all hosts, persistent, and have one of the following formats.

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naa.<number>

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t10.<number>

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eui.<number>

These formats follow the T10 committee standards. See the SCSI-3 documentation on the T10 committe Web site for information on Page 83.

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Path-based identifier. If the device does not provide the information on Page 83 of the T10 committee SCSI-3 documentation, 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 identifiers.

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.

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

vmhba<adapter>:C<channel>:T<target>:L<LUN>
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vmbh<adapter> is the name of the storage adapter. The name refers to the physical adapter on the host, not the SCSI controller used by the virtual machines.

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C<channel> is the storage channel number. Software iSCSI adapters and dependent hardware adapters use the channel number to show multiple paths to the same target.

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T<target> is the target number. Target numbering is determined by the host and might change if the mappings of targets that are visible to the host change. Targets that are shared by different hosts might not have the same target number.

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L<LUN> is the LUN number that shows the position of the LUN within the target. The number is provided by the storage system. If a target has only one LUN, the LUN number is always zero (0).

Legacy Identifiers

In addition to the SCSI INQUIRY or mpx identifiers, ESXi generates an alternative legacy name, called VML name, for each device. Use the device UID instead.