Command Information Unit; Table 5-21 Fcp 8-B Byte Lun - Sun Microsystems storagetek sl500 Reference Manual

FC-4 (FCP) Features

Command Information Unit

The Command Information Unit (T1) is a single-frame sequence.
The library supports the "first level addressing" LUN field as defined in SAM–2.
TABLE 5-21

TABLE 5-21 FCP 8-B byte LUN

Byte 0 Byte 1
00 LUN
For all commands that transfer data to the library:
FCP_DL (data length) in the FCP_CMND payload always equals the number of
bytes being transferred for the command.
For SCSI commands that specify the transfer length in blocks in the Command
Descriptor Block (CDB), the FCP_DL equals the Transfer_Length multiplied by the
Block_Size.
Note: If the FCP_DL value is less than the transfer length, then FCP_DL data will
be transferred and the command will be terminated with Check Condition. The
Sense Key will be 5h, the ASC will be 4Bh, and the ASCQ will be 80h.
For all commands that transfer data from the library:
The SCSI initiator is responsible for making sure the amount of data returned is
equal to the amount specified by FCP_DL—even if Good Status is returned. If the
amount does not match FCP_DL, a command-specific Upper Level Protocol
recovery action must be invoked. Because there are no transfers of Sequence
Initiative during read operations, once the SCSI Target receives the T1 Information
Unit, it may return Good Status, even though some of the data was not received by
the SCSI initiator. This can occur as the result of lost or corrupted frames in the
read data.
Note: The way a SCSI initiator determines the correct amount of data is returned
depends on the implementation and includes counting the number of bytes
returned and computing the number of bytes received by use of the relative offsets.
The FCP Command Reference Number (CRN) shall be used to ensure proper
ordering of Exchange's (SCSI commands). CRN usage is enabled based on I_T_L
nexus by setting the Enable Command Reference Number (ECRN) bit to 1b in the
FC Mode Page (19h) for the LUN. Task Management functions shall set the CRN
value to 0b. Refer to FCP-2 (4.3 Precise Delivery of SCSI Commands) for a detailed
description.
Note: The library currently does not support command queuing; thus CRNs are
not supported.
72 SL500: Interface Reference Manual • July 2008
illustrates this.
Byte 2 Byte 3
00 00
Byte 4 Byte 5
00 00
Byte 6 Byte 7
00 00
Revision: F • 96122