Host Driver Considerations - Quantum Scalar 218FC User Manual

LUN field, so that devices using SCC addressing can be used. In these cases, the bit fields used must be
manually configured.
For example, it may be desirable to address a FCP RAID controller using SCC Volume set addressing. In this
case, LUN 0 would be addressed by using the LUN value 0x4000. Using Logical Unit Addressing, the LUN
value would be 0x8000. Similarly, Bus 1, Target 2, LUN 3 would be represented as 0x8243.
SCSI Address
SCSI Bus 0, Target 0, LUN 0
SCSI Bus 0, Target 1, LUN 0
SCSI Bus 0, Target 2, LUN 0
(...)
SCSI Bus 0, Target 0, LUN 1
SCSI Bus 0, Target 1, LUN 1
SCSI Bus 0, Target 2, LUN 1
(...)
SCSI Target 7 Unavailable (Bridge Initiator ID)

Host Driver Considerations

There are a number of cases in which the host operating system or device driver expects a particular device
mapping. This is usually due to mappings being used from SCSI bus configurations. Some operating systems
map devices into internal tables that are represented as SCSI type BUS:TARGET:LUN triplets.
Applications that depend on this structure can be problematical. If a Fibre Channel driver is used that does
not use SCC mapping, typically devices are mapped at the Source ID (AL_PA) level to target devices in the
internal device map. This causes all devices behind the controller device to appear as LUNs to a single target.
This can have the effect of limiting the number of devices that a driver can support, or cause applications to
not address certain devices when they expect to be addressing target devices instead of LUN devices. Drivers
that support devices with multiple LUNs are particularly at risk. Flexibility in how devices are internally
mapped is necessary.
The ideal case is for host drivers to recognize controller devices from INQUIRY response data, and respond
by using SCC addressing to discover and map devices internally. In this type of environment, the
BUS:TARGET:LUN combination can map directly, with a possible offset to the Bus number from that used
on the FCR router.
SCSI-to-FCP Routing Table
FC Address
Loop ID 0, LUN 0x0000
Loop ID 1, LUN 0x0000
Loop ID 2, LUN 0x0000
(...)
Loop ID 16, LUN 0x0000
Loop ID 17, LUN 0x0000
Loop ID 18, LUN 0x0000
(...)
FC to SCSI Mapping 79