SCSI Send Diagnostic Command
Encyclopedia
The SCSI Send Diagnostic command is used to instruct a target device to perform a self-test on a specific LUN. The CDB
structure is:
The special parameter fields in the CDB have the following meaning:
SCSI CDB
In SCSI computer storage, commands are sent in a Command Descriptor Block .Each CDB can be a total of 6, 10, 12, or 16 bytes, but later versions of the SCSI standard also allow for variable-length CDBs. The CDB consists of a one byte operation code followed by some command-specific parameters.A...
structure is:
| bit→ ↓byte |
7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| 0 | Operation code = 1Dh | |||||||
| 1 | SELF-TEST CODE | PF | Reserved | SelfTest | DevOfl | UnitOfl | ||
| 2 | Reserved | |||||||
| 3–4 | Parameter list length | |||||||
| 5 | Control | |||||||
The special parameter fields in the CDB have the following meaning:
- PF - Page Format:
- 0 - SCSI-1 compliant (vendor-specific)
- 1 - SCSI-2 compliant (addresses a particular SCSI diagnostic pageSCSI diagnostic pagesSCSI target devices provide a number of SCSI diagnostic pages. These can be used by a Send Diagnostic command to tell a target device to run a specialised self-test. The Receive Diagnostic Results command is used where the results from the self-test operation are non-trivial.Most of the common...
) as defined in the parameter list. In this case the Send Diagnostic command is usually followed by a Receive Diagnostic ResultsSCSI Receive Diagnostic Results CommandThe SCSI Receive Diagnostic Results command is used to interrogate the results of a self-test. The self-test must have been triggered by a previous Send Diagnostic command which would have defined the self-test required. This is usually associated with one of the available diagnostic pages.The...
command.
- SelfTest if this bit is one then the device runs its default self-test. The device will then return either good status or a check condition. This version of the command is usually followed by a Receive Diagnostic Results command. If the SelfTest bit is zero then the device performs a special diagnostic operation as specified in the parameter list.
- DevOfL - Device Off-Line - used in high-availability applications - if this is one then the target is allowed to perform diagnostic operations that could cause it to fail read/write operations to the same from other initiators.
- UnitOfL - Unit Off-Line - similar to DevofL but refers to all LUNs