hesela.devSCSI Device Identification
SCSI Device Identification is the INQUIRY VPD page 0x83 mechanism for reporting typed identifiers associated with a logical unit, target port or target device.
A page can contain several designators with different associations; preserve the association, identifier type, code set and value together. A target-port designator does not identify the addressed logical unit merely because it appears in the same response. [1]
The SCSI reference distinguishes association 0 for the addressed device from associations 1 and 2 for the receiving port and containing target. It describes association-0 identification as consistent across other paths to that device. Vendor-specific type 0 is not guaranteed globally unique; do not infer uniqueness from the page number alone. [2]
systemd v257 scsi_id selects logical-unit-associated descriptors for the device identifier while handling target-port-group information separately. This is a version-specific selection policy, not a rule that the first descriptor is always the correct identifier. [3]
In systemd v257, a binary NAA designator is rendered in ID_SERIAL as the type digit 3 followed by the hexadecimal identifier. Thus 36... begins with a host-format prefix 3 and an NAA value starting 6; ID_SERIAL_SHORT omits that type prefix. This is a pinned implementation's representation, not a universal WWID format. [3] [4]
RFC 8154 restricts pNFS SCSI volume identifiers to association 0 and four allowed designator types. Several descriptors may still share association, code set and type; clients must examine all descriptors for a match to the supplied code set, designator type and value. This is pNFS matching against a supplied identity, not scsi_id's selection of a preferred host identifier. [5]
Relations
- related
- SCSI logical unit (LU), SCSI Unit Serial Number, World Wide Name (Fibre Channel), Multipath I/O
Citations
- Douglas Gilbert: sdparm 1.12 documentation, VPD pages and descriptor associations
- Seagate SCSI Commands Reference Manual, 100293068 Rev. L (November 2020), sections 5.4.9 and 5.4.22
- systemd v257: scsi_serial.c, check_fill_0x83_id, do_scsi_page80_inquiry and scsi_get_serial
- systemd v257: scsi_id.c, sanitized ID_SERIAL and ID_SERIAL_SHORT exports
- RFC 8154 (May 2017), section 2.3.1: pNFS SCSI volume identification and descriptor matching
Sources & caveats
- Primary documentation and pinned implementation review on 2026-11-03; no device interrogation, failover experiment or global-uniqueness measurement.