Specifications

17 ATTO Technology FibreBridge 4500 Installation and Operation Manuall
3.2 Handling multiple initiators
Several Fibre Channel hosts or initiators may initiate commands through the FibreBridge to SCSI devices. The
basic mechanism to resolve possible conflicts among initiators is to use SCSI
Reserve and Release commands.
A Fibre Channel host may need exclusive access to a
SCSI device. SCSI
Reserve and Release commands
allow logical units to be reserved or released under
host control.
The FibreBridge intercepts any Reserve or Release
command from a Fibre Channel host, performs initial
processing and, if appropriate, relays the Reserve
command to the SCSI device.
In a FibreBridge environment, the identity of the
initiator (WWN) is not relayed to the SCSI device. A
two-step process addresses initiator identity in the
FibreBridge, and reserves the SCSI device on behalf of
the FibreBridge.
Initiators on both the Fibre Channel (via the
FibreBridge) and on the SCSI bus may initiate reserve
and release commands to the SCSI devices.
The FibreBridge processing of reserve and release
commands involves two tiers of verification. The first
tier is within the FibreBridge; the second tier is within
the SCSI device.
1 The FibreBridge receives a SCSI Reserve
command.
Tier 1
2 The FibreBridge determines, via its
internal database, whether there are
conflicting concurrent reservations from
Fibre Channel hosts for the target SCSI
device.
3 If there is a conflict, the FibreBridge
returns a check condition with
reservation conflict to the initiator.
4 If there is no conflict, the FibreBridge
marks the SCSI device as reserved in its
internal database.
Tier 2
5 The FibreBridge relays the Reserve
command to the SCSI device.
6 The SCSI device determines whether it is
already reserved.
7 If the SCSI device is already reserved, it
returns a reservation conflict to the
FibreBridge. The FibreBridge removes
its reserved indicator in its internal
database, and returns reservation conflict
to the initiator.
8 If the SCSI device was not previously
reserved, the SCSI device is reserved
and returns success to the FibreBridge.
The FibreBridge then returns success to
the initiator.
The FibreBridge does not implement extent
reservation.
Single initiator
A single initiator presents no conflicts.
1 A single Fibre Channel initiator sends
the Reserve command through the SAN
to the FibreBridge
2 The FibreBridge determines that no
reservation conflict exists at Tier 1.
3 The FibreBridge sends the Reserve
command to the SCSI target.
4 The SCSI target is reserved until a
Release command is sent by the Fibre
Channel initiator.
FC Initiator 1
SCSI target
ATTO FibreBridge 1
Fibre Channel
Arbitrated Loop or
Fabric
Single Initiator