The 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...

 Inquiry command is used to obtain basic information from a 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 is:

bit→ ↓byte	7	6	5	4	3	2	1	0
0	Operation code = 12h
1	LUN			Reserved				EVPD
2	Page code
3	Allocation length (MSB)
4	Allocation length (LSB)
5	Control

If the EVPD parameter bit is zero and the Page Code parameter byte is zero then the target will return the standard inquiry data, which is structured as follows:

bit→ ↓byte	7	6	5	4	3	2	1	0
0	Peripheral qualifier			Peripheral device type
1	RMB	Device-type modifier
2	ISO version		ECMA version			ANSI-approved version
3	AEC	TrmIOP	Reserved		Response data format
4	Additional length (n-4)
5	Reserved
6	Reserved
7	RelAdr	WBus32	WBus16	Sync	Linked	Reserved	CmdQue	SftRe
8–15	Vendor identification (ASCII)
16–31	Product identification (ASCII)
32–35	Product revision level
36–55	Vendor-specific
56–95	Reserved
96	Vendor-specific parameters (variable number of bytes)

The special fields in the standard inquiry data have the following meaning:

• Peripheral Device Type - see separate article on SCSI Peripheral Device Type
  SCSI Peripheral Device Type
  A SCSI Peripheral Device Type is a way of describing what capabilities are provided by a SCSI device. It is a five-bit field which can be found in the first byte provided in response to an Inquiry Command...
  
  s
• RMB - removable medium
• AENC - 1 = supports Asynchronous Event Notifications - (processor devices only)
• TrmIOP - 1 = supports Terminate I/O Process messages
• Response data format - 000=SCSI compliant, other values = legacy devices
• RelAdr - 1= this LUN supports Relative Addressing Mode (linked commands only)
• WBus32+WBus16 - support for wide data buses:
  • 00 - 8-bit only
  • 01 - 8 or 16-bit
  • 11 - 8, 16 or 32 bit
• Sync - 1 = supports synchronous transfers
• Linked - 1 = this LUN supports linked commands
• CmdQue - 1 = supports Tagged Command Queuing
• SftRe - 1 = performs soft resets

If the EVPD parameter bit is one then the target will return Vital Product Data

Vital Product Data

Vital Product Data is a collection of configuration and informational data associated with a particular set of hardware or software. Vital product data stores information such as part numbers, serial numbers, and engineering change levels. Not all devices attached to a system will provide...

(VPD). This can be from one of a number of different pages, depending on the value of the Page Code parameter:

• 00h - Supported vital product data
• 01h-7Fh - ASCII information
• 80h - Unit serial number
• 81h - Implemented operating definitions (Obsolete)
• 82h - ASCII implemented operating definition (Obsolete)
• 83h - Device Identification
• 84h - Software Interface Identification
• 85h - Management Network Addresses
• 86h - Extended INQUIRY Data
• 87h - Mode Page Policy
• 88h - SCSI Ports
• 89h-AFh - Reserved
• B0h-BFh - Device type specific
• C0h-FFh - Vendor-specific