The SCSI Log Sense command is used to obtain current data from log pages

SCSI log pages

SCSI target devices provide a number of SCSI log pages. These can be interrogated by a Log Sense command and in some cases can be set by a Log Select command. The Log Sense and Log Select commands include a 6-bit address field, allowing for 64 possible log pages. There is a standard map of log...

 in a SCSI

SCSI

Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...

 target device. The CDB

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 for the Log Sense command is:

SCSI Log Sense

bit→ ↓byte	7	6	5	4	3	2	1	0
0	Operation Code = 0x4D
1	LUN Reserved						Obsolete	SP
2	PC		PAGE CODE
3	SUBPAGE CODE
4	Reserved
5	PARAMETER POINTER
6
7	ALLOCATION LENGTH
8
9	Control

The special parameter fields in the CDB have the following meaning:

• SP - Save Parameters - if this is one then the target should save all saveable log parameters to a non-volatile memory or media area.

• PC - Page Control - this indicates which type of values should be returned:
  • 00 - Current Threshold Values
  • 01 - Current Cumulative Values
  • 10 - Default Threshold Values
  • 11 - Default Cumulative Values

• Parameter Pointer indicates the first parameter code to be returned.

• Allocation Length in bytes

If the Parameter Pointer is zero and the Allocation Length is large enough then all parameters are returned.