hesela.devSCSI Unit Attention
SCSI Unit Attention is a condition that notifies an initiator of a relevant logical-unit or target state change.
Identity: Its sense key is 06h, distinct from CHECK CONDITION status 02h. ASC/ASCQ qualifies the change: 29h/00h combines power-on and reset possibilities, while 2Ah/09h reports changed capacity data. These codes do not isolate a failed component. [1] [2]
Observation: In Linux v6.12 target code, pending conditions are held on an initiator-mapped device entry. The REQUEST SENSE clearing helper selects the first queued pair, described by the code as highest priority, and removes all pending conditions from that entry. This is a version-specific implementation, not a universal device rule or a passive event-history query. [3]
Handling: Linux v6.12 can select a retry for an expected reset notification, but preserves the 28h/00h medium-change exception in that branch. Do not infer an unconditional retry policy from the key alone. [4]
Response length: In that same target implementation, a request with the DESC bit set is rejected before the clearing helper runs. Buffer-mapping failure also returns before that helper. Once reached, the helper clears pending conditions before the length-limited payload copy. A short successful response therefore need not retain every field needed to interpret the consumed notification. [6]
Identity query: The cited SCSI reference specifies that INQUIRY runs without clearing a pending Unit Attention. An identity response is therefore not evidence that the notification was consumed. Its UA_INTLCK_CTRL table separately distinguishes clearing from retention after CHECK CONDITION reporting; clearing policy is device-dependent. That retention does not make REQUEST SENSE non-consuming: Table 454's footnote says it still clears the reported condition. [7]
Relations
- related
- SCSI, SCSI sense data, SCSI sense key, SCSI CHECK CONDITION, Additional sense code, Additional sense code qualifier
Citations
- T10 SCSI sense-key assignments (informative, dated 18 May 2012)
- T10 ASC/ASCQ assignments, list dated 28 November 2024
- Linux v6.12 target: target_scsi3_ua_check and core_scsi3_ua_clear_for_request_sense
- Linux v6.12: scsi_report_sense and scsi_check_sense; disposition is not device command status
- Linux v6.12 target: spc_emulate_request_sense, validation and copy ordering
- Seagate SCSI Commands Reference Rev. L (November 2020), INQUIRY p. 104 and UA_INTLCK_CTRL Table 454 p. 464
Further reading
Sources & caveats
- T10 online assignments are informative; the applicable written standard takes precedence.
- No device reset, recovery test or failure-rate measurement was performed.