Electrical computers and digital data processing systems: input/ – Input/output data processing – Peripheral monitoring
Reexamination Certificate
2000-11-29
2004-04-06
Elamin, Abdelmoniem (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
Peripheral monitoring
C710S120000, C709S208000, C709S211000, C709S230000, C709S227000, C709S241000, C709S241000
Reexamination Certificate
active
06718402
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to data and information communication systems and their operation, and, more particularly, to communications networks, including a Fibre Channel network. Even more particularly, the present invention relates to a method and system for maintaining a persistent unit attention signal in a Fibre Channel storage router in a multi-initiator Fibre Channel network.
BACKGROUND OF THE INVENTION
In a Fibre Channel-to-SCSI router architecture, one SCSI initiator (interface), such as a SCSI router, can speak to multiple SCSI targets on behalf of many Fibre Channel (“FC”) initiators (hosts). The SCSI router provides an interface to efficiently manage commands and communications between the FC initiators and the SCSI targets. On the SCSI side of the network, each SCSI target is only aware of the SCSI router interface to which it is directly attached, and likewise, on the FC side of the network, each FC host sees only the SCSI router as a target. Neither the FC hosts nor the SCSI targets are aware of targets or hosts, respectively, on the other side of the SCSI router to which they are connected.
A Fibre Channel-to-SCSI router thus provides a pass-through data management role. For example, when a Fibre Channel host issues a command to a SCSI target, the SCSI router receives the command and forwards it to the target. To the FC host, the SCSI router is the target, and the data management role provided by the SCSI router is transparent to the host. Similarly, the SCSI target on the other side of the SCSI router sees the SCSI router to which it is attached as the initiator of the command. The data management role provided by the SCSI router is, likewise, transparent to the SCSI target. The situation is similar when it is the SCSI target sending a signal to a FC initiator through a SCSI router.
As part of their data management role, SCSI routers in a Fibre Channel-to-SCSI network can receive unit attention signals intended for a Fibre Channel host from a SCSI target. A unit attention signal is a signal sent out by a SCSI target to inform a host of the SCSI target's current status. In general, a SCSI target will issue a unit attention signal if it undergoes some change in status of which hosts on the network should be aware. For example, a SCSI target may want to inform all hosts communicating with it that it has been rebooted, or has gone off-line and come back on-line, sometime between the last communication between the SCSI target and one or more hosts. There can be different kinds of unit attention signals.
In current multi-initiator Fibre Channel-to-SCSI networks, however, not all Fibre Channel initiators querying a SCSI target will receive a unit attention signal issued by the SCSI target. This is because each SCSI target sees the SCSI router interface as the only initiator in the network. A SCSI target will issue only a single unit attention signal to each host upon receiving a communication, such as a command, from the host. Therefore, because a SCSI target sees the SCSI router as the only host on the FC side of the network, the first command from any FC host will elicit a unit attention signal from the SCSI target, but subsequent commands from other hosts will not, because the SCSI target sees all commands as originating from the SCSI router. A SCSI target in prior art Fibre Channel-to-SCSI networks will thus issue only a unit attention signal upon receiving the first command following a status changing event, but will issue no subsequent unit attention signals for the same status changing event.
Current Fibre Channel-to-SCSI routers thus do not provide a means by which all affected Fibre Channel hosts can receive a unit attention signal from a SCSI target that has undergone a status changing event. The Fibre Channel hosts in such prior art networks might, therefore, continue to behave as if they are in a particular relationship with a SCSI target when in fact the relationship has changed. The result of this confused state can lead to data corruption, component failure, and/or other unpredictable results within a Fibre Channel-to-SCSI network.
In particular, if a Fibre Channel host and a SCSI target are in a reserve relationship, a change in SCSI target status, such as a power loss, can result in the loss of the reserve relationship. This situation is more fully described in “Method and System for Maintaining Reserve Command Relationships in a Fibre Channel Network” disclosed in related U.S. patent application Ser. No. 09/251,759, filed on Feb. 18, 1999 (the “Maintaining Application”) now U.S. Pat. No. 6,138,161, which is hereby incorporated by reference. For example, after recovering from a power loss, a SCSI target may receive a command from a Fibre Channel host other than the host with which it was previously in a reserve relationship. The SCSI target will issue a unit attention signal to the host issuing the command. For the reasons discussed above, with prior art SCSI routers, the unit attention signal will not be forwarded to the first Fibre Channel host. The Fibre Channel host that was in a reserve relationship with the SCSI target will thus be unaware of the loss of the reserve relationship and will not attempt re-establish that relationship. Therefore, other Fibre Channel hosts will be able to issue commands to the SCSI target, which the SCSI target will execute because it is no longer in a reserve relationship.
A SCSI target that has undergone and recovered from a status changing event and subsequently receives a command from a Fibre Channel host can execute the command and send out a unit attention signal. In this case, the unit attention signal acts only as an information mechanism. More typically, however, a SCSI target will issue a unit attention signal in response to a command from a host received while the target is still in an error condition. In such a case, the FC host can either reissue the command at a later time, or it can deal with the error condition in some other way. If the command is reissued while the SCSI target is still in an error condition, a different type of unit attention, or other error signal, can be issued in response by the target.
In prior art SCSI routers, if a FC host “A” is in a reserve relationship with a SCSI target, and the SCSI target undergoes a status changing event such that the reserve relationship is lost, several situations might develop. For example, a second Fibre Channel host “B” may be the first host to issue a command to the SCSI target after the status changing event. In response, the SCSI target will issue a unit attention signal through the SCSI router to FC host B. If the SCSI target rejects the command, FC host B might reissue the command. If FC host A issues a command subsequent to the command from FC host B, the SCSI target will not recognize FC host A as a separate host and will not issue a unit attention signal to FC host A. FC host A will be unaware that its reserve relationship with the SCSI target has been lost. Furthermore, If FC host B establishes a new reserve relationship with the SCSI target, FC host A will subsequently have its commands rejected by the SCSI target.
If, on the other hand, FC host B does not establish a reserve relationship with the SCSI target, commands from FC host A received after the SCSI target :z recovers might be executed simply because the SCSI i target is available, and not because the original reserve relationship still exists. FC host A will be unaware that the reserve relationship has lapsed and will continue to operate as if the reserve relationship still exists.
The SCSI target device in the above example will therefore go from a reserve relationship with FC host A, to being available to all FC hosts on the network on a first-come, first-served basis. The potential then exists for conflicts in commands to the SCSI target device. In particular, if the SCSI target device is a sequential access device, such as a tape drive, commands received while a previous command is executing can result in a loss of data, component
Crossroads Systems Inc.
Elamin Abdelmoniem
Gray Cary Ware & Freidenrich LLP
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