ATTO Technology 2100R, 2200R/D, 3200R Fibre Channel to SCSI Address Mapping, Address Descriptors

ATTO Technology, Inc. ATTO FibreBridge Installation & Operation Manual

This default method of addressing was developed with the assumption that not all host adapter manufacturers have designed the hierarchical addressing methodology into their products yet. Since the bit positions here are also easily modified in non-volatile RAM, this addressing will work with all host adapters that only use one byte of LUN addressing.

Fibre Channel to SCSI Address Mapping

Hosts send commands to the FibreBridge (and attached SCSI devices) by sending FCP_CMND (Fibre Channel Command) Frames to the AL_PA assigned to the FibreBridge during loop initialization. Each FCP_CMND frame contains an 8-byte FCP_LUN field. The first level addressing field of the FCP_LUN provides the three SCSI addressing components required to uniquely address a device. FCP_LUN addressing levels 2 – 4 are ignored.

Address Descriptors

The Bus, Target, and LUN fields are set up using Address Descriptors. The SCSI Architecture Model specification provides a guideline mapping the FCP_LUN first level addressing field into SCSI addressing components. The FibreBridge uses user configurable Address Descriptors to effect this translation.

The FibreBridge contains an Address Descriptor for the Peripheral Device, Virtual Device, and Logical Unit addressing methods. The Addressing Method specified in the FCP_LUN (bits 15-14) selects the appropriate Address Descriptor.

Each Address Descriptor defines the size and location of each of the three SCSI addressing components within the FCP_LUN first level addressing field. One hexadecimal digit is assigned to each of Bus, Target, and LUN, with the left 4 bits indicating the rightmost bit-position of the respective field, and the right 4 bits indicating the width of that field. Address Descriptors therefore are three bytes in length, <bus><lun><target>.

For example, an address descriptor 820344 defines the bus (82), LUN (03), and target (44) components. This bus component is a 2 bit field starting in bit-position 8; the LUN component is a 3 bit field starting in bit-position 0; and the target component is a 4 bit field starting in bit-position 4. Additional addressing examples representing typical configurations are provided below. The translation process masks off any unmapped bits, and as a corollary, not all fields need to be mapped. Fields must be contiguous (e.g. bllttb is not permitted - the bus field may not be split).

FibreBridge Address Descriptors are stored in non-volatile memory. They are field configurable using SCSI WRITE/READ BUFFER commands or through ATTO BridgeTools software.

BridgeTools is the preferred method to set the Address Descriptor fields because of the supplied graphical user interface.

SCSI-3 Command Changes for Hierarchical Addressing Support

The FibreBridge supports a limited set of SCSI commands directly, as described in Commands documentation (see References above). A brief description of addressing-related aspects for commands follows.

SCSI-3 INQUIRY Command

The Inquiry Data returned in the response from the SCSI-3 Inquiry command issued to the FibreBridge includes the HiSupport bit set to 1. This indicates that the FibreBridge supports hierarchical addressing,

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