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3.0.1 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.
General verification procedure
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.
Arbitrated Loop or
FC Initiator 1
65
ATTO Technology Inc. FibreBridge Installation and Operation Manual
Single Initiator
Fibre Channel
Fabric
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.
ATTO FibreBridge 1
SCSI target
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