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BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to channel and network communication systems
and processes and, in particular, to a system and method for automatic
dynamic loop address changing in a Fibre Channel environment.
2. Description of Related Art
There are two kinds of protocols for device communication: channels and
networks. Channels, for example, between a master host computer and a
slave peripheral device, transport a large amount of data at very high
speeds over relatively small distances with little software overhead once
data transmission commences. A channel provides a direct or switched
point-to-point connection between a master and a slave that is
hardware-intensive. Networks, on the other hand, usually interface many
users and support many transactions, sharing a plurality of hosts and
system resources, over medium to large distances. In network connections
higher software overhead is generally acceptable as long as high
connectivity is achieved.
The Fibre Channel Protocol ("FCP") is a new generation protocol that
combines the best of these two disparate methods of communication in a
single Open-Systems-Interface-like (OSI-like) stack architecture.
Essentially, the Fibre Channel ("FC") is a multi-topology, multi-layer
stack with lower-layer-protocols ("LLPs") for controlling the physical
transport characteristics and upper-layer-protocols ("ULPs") for mapping
LLP communication to and from higher-level software structures that are
compatible with an Operating System. These ULPs include both channel and
network protocols such as Intelligent Peripheral Interface ("IPI"), Small
Computer System Interface ("SCSI"), and Internet Protocol ("IP"), among
others.
One of the most desirable objectives in any multi-device communication
system is the ability to "hot-plug," that is, the capability to delete,
add, and/or substitute a device in a system without bringing the system
down or incurring an inordinate amount of specialized software overhead.
For example, in a master-slave channel communication system, it is
extremely useful to be able to change the attached peripheral devices on
the fly without having to re-boot the system or without erecting expensive
software partitions between the Operating System and the protocol that is
associated with the multi-device communication system.
Although the ULPs in the FCP stack offer the benefits of multi-protocol
connectivity to both channel and network communication systems, they do
not provide for the capability to dynamically alter the device
configuration of the system without the aforementioned shortcomings.
Moreover, many Operating Systems currently in use do not provide for
structures that would facilitate dynamic reconfiguration of the devices
disposed in an FC environment. Accordingly, it can be appreciated that
because of the tremendous growth potential for FC-compatible computer
systems, there is a manifest need for providing a cost-effective solution
that ameliorates these and other drawbacks.
SUMMARY OF THE INVENTION
The present invention overcomes the above-identified problems as well as
other shortcomings and deficiencies of existing technologies by providing;
for a computer system operable with an Operating System (OS), the computer
system having a Fibre Channel (FC) communication environment, which
environment includes a plurality of FC devices, at least one of the FC
devices being an initiator; a method for dynamically controlling the
configuration of the plurality of FC devices, which method comprises the
steps of: determining an FC-specific information structure related to each
of the plurality of FC devices; associating the FC-specific information
structure for each of the plurality of FC devices with a logical link
element compatible with the Operating System, the associating step being
effectuated by association means; and updating the association means
responsive to a reconfiguration of the FC environment.
The present invention further provides a system for dynamically controlling
the configuration of a multi-device FC communication environment, the
system comprising: means for determining an FC-specific information
structure related to each of the plurality of FC devices; means for
associating the FC-specific information structure for each of the
plurality of FC devices with a logical link element compatible with the
Operating System of a computer system; and means for updating the
associating means responsive to a reconfiguration of the FC environment.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention may be had by
reference to the following Detailed Description when taken in conjunction
with the accompanying Drawings wherein:
FIG. 1 illustrates a block diagram of a prior art channel communication
system, more particularly, a system operable with a SCSI standard;
FIG. 2 illustrates a block diagram of an exemplary computer system wherein
the teachings of the present invention may be practiced;
FIG. 3 depicts a diagrammatic representation of the Fibre Channel (FC)
Protocol stack;
FIGS. 4A-4C depict block diagrams of the three topological configurations
available for Fibre Channel Nodes;
FIG. 5 illustrates an exemplary embodiment of the mapping method in
accordance with the teachings of the present invention;
FIG. 6 depicts an exemplary flow diagram for a method of automatic dynamic
loop address changing in accordance with the teachings of the present
invention; and
FIGS. 7A and 7B depict an exemplary embodiment where a loop address is
dynamically changed in accordance with the teachings of the present
invention upon introduction of a hard-coded device in the loop.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to the drawings wherein like or similar elements are
designated with identical reference numerals throughout the several views,
and wherein the various elements depicted are not necessarily drawn to
scale, and, in particular, to FIG. 1, there is shown a block diagram of a
prior art channel communication system, generally at 100, such as a
channel system operable with the Small Computer System Interface ("SCSI")
protocol. A processor 110 is provided with a SCSI adapter 115 in order to
effectuate channel communication via a SCSI bus 125 to which a plurality
of peripheral devices, for example, SCSI devices 120A-120G, are connected.
It can be appreciated by those skilled in the art that although not
depicted in FIG. 1, the ends 130A and 130B of the SCSI bus 125 may each
contain an appropriate termination element, respectively.
As is well-known in the art, a SCSI device can be either an initiator or a
target and the SCSI bus 125 can include any combination thereof provided
at least one initiator and one target are present. For example, the
processor 110, through its adapter 115, may function as the initiator and
the device 120D may function as a target in the channel communication
system 100. Certain specific functions are assigned to either an initiator
or a target: (i) an initiator can arbitrate for the bus 125 and select a
target; (ii) a target can request the transfer of command, data, status,
or other information to or from the initiator, and (iii) in some
instances, a target can arbitrate for the bus 125 and reselect an
initiator to continue a bus transaction.
Continuing to refer to FIG. 1, the target 120D may support from one to
eight physical or virtual devices called "logical units." A complete
device address consists of the SCSI identity ("ID") of the target and the
Logical Unit Number ("LUN") of the device. A physical device that does not
support additional logical units such as for example, a conventional SCSI
hard disk drive, comprises only one logical unit in which case the LUN is
set to zero.
In a SCSI environment, a bus transaction is defined by the SCSI command
protocol as an input/output ("I/O") process. An I/O process begins with
the establishment of a logical link called a "nexus," which defines the
logical path between an initiator and a target such as a conventional SCSI
hard disk drive, represented by the SCSI ID of the initiator ("I") and the
SCSI ID of the drive ("T"). As is understood in the art, the nexus may be
further refined by using the IDENTIFY message of the SCSI command protocol
to include a LUN if applicable. In this case, the complete logical link
will be I.sub.-- T.sub.-- LUN. It should be understood that the I.sub.--
T.sub.-- LUN logical link is sometimes interchangeably referred to as the
BUS.sub.-- TARGET.sub.-- LUN or B.sub.-- T.sub.-- LUN also.
Referring now to FIG. 2, a block diagram of an exemplary computer system
200 is depicted wherein the teachings of the present invention may be
practiced. As can be appreciated by those skilled in the art, the computer
system 200 is represented in FIG. 2 in its functional aspects. An
Operating System ("OS") 210 is operably provided in the computer system
200 to control the information flow associated therewith. The OS 210 may
be a Disk Operating System ("DOS") or a Network Operating System ("NOS")
such as, for example Windows NT.RTM. or NetWare.RTM., as may be
appropriate depending upon whether the computer system 200 is arranged in
a network configuration.
The OS 210, moreover, is operable with at least a conventional channel
communication interface such as, for example, the SCSI interface standard
described above. The exemplary OS 210 may further be provided with such
functional structures that would enable interoperability with conventional
network communication protocols such as, for example, the Internet
Protocol ("IP").
Continuing to refer to FIG. 2, the exemplary OS 210 communicates with an
OS-compatible channel or network communication protocol/interface 215 via
an upper.sub.-- level.sub.-- communication path 230. It should be
appreciated that the upper.sub.-- level.sub.-- communication path 230 in
the functional block representation of the exemplary computer system 200
may encompass such OS-software structures as communication protocol
drivers, for example, the SCSI protocol drivers or IP protocol drivers.
The exemplary OS 210 and the OS-compatible interface/protocol 215 together
constitute what will be henceforth referred to as an OS environment 250 in
the computer system 200. Reference numeral 220 refers to a Fibre Channel
("FC") environment which may encompass a plurality of FC devices operable
in accordance with the teachings of the present invention in addition to
the known Fibre Channel Protocol ("FCP") architecture described below in
further detail.
Still continuing to refer to FIG. 2, it should be understood that most
Operating Systems including, for example, the OS 210, are not provided
with the capability of communicating "directly" with the devices disposed
in the FC environment 220. Therefore, in order to operably include and
harness the benefits of the FC environment 220 in an exemplary computer
system 200, a link path 225 is provided between the FC environment 220 and
the OS-compatible communication interface 215. As will be appreciated by
those skilled in the art upon reference hereto, providing the link path
225 in accordance with the teachings of the present invention between the
FC environment 220 and the OS-compatible communication interface 215
facilitates dynamic address changing of the FC devices, which changing is
transparent to the OS-compatible upper-level software structures.
Referring now to FIG. 3, a diagrammatic representation of the FCP stack
architecture is shown generally at 300. As can be readily appreciated, the
FCP architecture is structured as a hierarchical set of protocol layers,
much like the Open Systems Interface ("OSI") stack. The three bottom
layers of the FC stack (layer 310, labeled as FC-0, through layer 320,
labeled as FC-2) form what is known as the Fibre Channel Physical Standard
("FC-PH"). This Standard defines all the physical transmission
characteristics of a Fibre Channel environment including, for example, the
FC environment 220 (shown in FIG. 2). The remaining layers (layer 325,
labeled as FC-3 and layer 330, labeled as FC-4) handle interfaces with
other network protocols and applications. Unlike the existing Local Area
Network ("LAN") technologies such as Ethernet and Token Ring, FC keeps the
various functional layers of the stack 300 physically separate. As can be
appreciated, this physical separation enables implementation of some stack
functions in hardware and others in software or firmware.
The layer 310, FC-0, is the lowest functional layer of the FC architecture
and describes the physical characteristics of the link connections among
the plurality of FC devices disposed in the FC environment 220 (shown in
FIG. 2). FC-0 supports a basic rate of 133 Mbaud, the most commonly used
speed of 266 Mbaud, as well as 531 Mbaud and 1.062 Gbaud. However, because
of the overhead involved in establishing and maintaining link connections,
the actual data throughput is somewhat lower: 100 Mbit/s for 133 Mbaud,
200 Mbit/s for 266 Mbaud, 400 Mbit/s for 531 Mbaud, and 800 Mbit/s for
1.062 Gbaud. Further, FC-0 supports a wide range of physical cabling,
including single-mode or multimode fiber-optic cable, coaxial cable, and
shielded twisted pair ("STP") media. Each of these cabling elements
supports a range of data rates and imposes specific distance limitations,
but FC can mix all of them within the same FC environment such as the FC
environment 220 shown in FIG. 2. For instance, single-mode optical fiber
could be used for distances up to 10 km; multimode fiber, at 200 Mbit/s,
could be used for distances up to 2 km; and STP, which supports 100
Mbit/s, may be used for up to 50 meters.
The layer 315, FC-1, defines the transmission protocol, including the
serial encoding and decoding rules, special characteristics, and error
control. FC-1 uses an 8B/10B block code, where every 8 data bits are
transmitted as a 10-bit group with two extra bits for error detection and
correction, known as disparity control. The 8B/10B scheme supplies
sufficient error detection and correction to permit use of low-cost
transceivers, as well as timing recovery methods to reduce the risk of
radio-frequency interference and ensure balanced, synchronized
transmissions.
The third layer of the FC-PH, layer 320, FC-2 describes how data is
transferred between the FC devices, each FC device being disposed at a
"Node," and includes the definition of the frame format, frame sequences,
communications protocols, and service classes. The basic unit of data
transmission in Fibre Channel is a variable-sized frame. Frames can be up
to 2,148 bytes in length, comprising a payload of up to 2,048 bytes; 36
bytes of overhead that provides framing, source and destination port
addressing, service type, and error detection information; and up to 64
bytes of additional optional overhead for other miscellaneous information
about the user data, that is, the payload. A single higher layer (that is,
the upper layers in the stack 300) protocol message may be larger than a
frame's payload capacity, in which case, the message will be fragmented
into a series of related frames called a sequence.
Continuing to refer to FIG. 3, FC-2 layer can be appreciated as the main
"workhorse" of the FCP stack 300. It frames and sequences data from the
upper layers (layers 325 and 330) for transmission via the FC-0 layer; it
accepts transmissions from the FC-0 layer and reframes and resequences
them, if necessary, for use by the upper layers 325 and 330. In addition
to defining full duplex transmission path between two nodes, the FC-2
layer also provides essential traffic management functions, including flow
control, link management, buffer memory management, and error detection
and correction. An important feature of the FCP stack 300 is that the FC-2
layer defines four classes of service to meet a variety of communication
needs. Class 1 Service defines hard-wired or circuit-switched connections
that are dedicated, uninterruptible communication links. This service
provides exclusive use of the connection for its duration (sometimes
called a "selfish connection") . Class 1 Service is designed for
time-critical, "non-bursty" dedicated links, such as those between two
supercomputers. Class 2 Service is a connectionless, frame-switched
transmission that guarantees delivery and confirms receipt of traffic.
Like conventional packet-switching technologies such as frame relay, Class
2 switching is performed on the FC data frame rather than on a connection.
No dedicated connection is established between the nodes; each frame is
sent to its destination over any available route. When congestion occurs
in Class 2 traffic, the frame is retransmitted until it successfully
reaches its destination. Class 3 Service defines one-to-many
connectionless frame-switched service that is similar to Class 2 Service,
except that it has no delivery guarantee or confirmation mechanism. It can
be appreciated that Class 3 transmissions are faster than Class 2
transmissions because they do not wait for confirmation. But if a
transmission does not arrive at its destination, Class 3 Service does not
retransmit. This service is most often used for real-time broadcasts that
cannot wait for acknowledgment but are not sufficiently time-critical to
warrant Class 1 Service. It is also used for applications that can
tolerate lost frames. Class 4 Service is a connection-based service that
offers guaranteed fractional bandwidth and guaranteed latency levels.
The FC-3 layer, layer 325, provides a common set of communication services
of higher layer protocols above the FC-PH level. These additional services
may include, for example, mechanisms for multicast and broadcast data
delivery, "hunt" groups wherein more than one target node can respond to a
given initiator node, and multiplexing multiple higher layer protocols and
the FC-PH.
The top layer, layer 330, of the FCP stack 300 is the FC-4 layer. It
defines the higher layer applications that can operate over an FC
infrastructure such as, for instance, the FC environment 220 shown in FIG.
2. The FC-4 layer provides a way to utilize existing channel and network
protocols over Fibre Channel without modifying those protocols.
Accordingly, the FC-4 layer acts like a protocol convergence layer so that
the FC node appears to provide the exact lower-layer transport services
that the higher-layer channel or network protocol requires. This
convergence function may require that the FC-4 provide additional services
such as buffering, synchronization, or prioritization of data. It can be
appreciated that the FC-4 functionality is encompassed in the link path
225 disposed between the FC environment 220 and the OS-compatible
interface 215 of the exemplary computer system 200, shown in FIG. 2.
Still continuing to refer to FIG. 3, various FC-4 level mappings have been
specified for a number of higher layer channel and network communication
protocols, including: Intelligent Peripheral Interface ("IPI"); SCSI;
High-Performance Parallel Interface ("HIPPI"); Single Byte Command Code
Set ("SBCCS"); Logical Link Control ("LLC"); IP; and Asynchronous Transfer
Mode ("ATM") Adaptation Layer ("AAL") However, as indicated hereinabove,
these mappings do not provide for dynamic address changing of the FC
devices that are disposed in the FC environment 220 (shown in FIG. 2) is
operable in accordance with the FCP stack 300.
Referring now to FIGS. 4A-4C, three exemplary topological configurations
are shown, generally at 490, 491, and 492, respectively, into which the FC
Nodes may be arranged. It should be understood that all three topologies
are fully interoperable and the teachings of the present invention may be
practiced in any appropriate combination thereof.
An FC Node is an entity, system, or device that has the capability to
process the ULPs, FC-3, and some of the FC-2 functions. A Node may contain
one or more Ports, commonly known as Node Ports or N.sub.-- Ports. An
N.sub.-- Port is a hardware entity within a Node that supports the FC-PH.
It may act as an originator (that is, an initiator), or a responder (that
is, a target), or both. Hereinafter, the terms nodes, devices and ports
will be somewhat interchangeably used for the purposes of the present
invention.
Reference numeral 490 refers to a point-to-point topology which utilizes
communication links 410A, 410B to provide a full duplex transmission path
between any two FC Nodes, denoted here as N.sub.-- Ports 400A and 400B.
This connection topology provides the maximum possible bandwidth and
lowest latency since there are no intermediate devices/Nodes.
Reference numeral 492 refers to a switched fabric topology where each FC
device or node (N.sub.-- Port) is connected to an F.sub.-- Port that is
part of a fabric, for example fabric 430, and receives a non-blocking data
path to any other connection on the fabric. The fabric 430 may be a switch
or series of switches and is responsible for routing between Nodes, error
detection and correction, and flow control. The operation of the fabric
430 is independent of the higher layer communication protocols, largely
distance-insensitive, and may be based on any technology.
Communication paths, for example, path 437, provide a bidirectional
connection between a Node, N.sub.-- Port 440 and a fabric port (F.sub.--
Port) 436. The switched fabric topology 492 provides the maximum
connection capability and total aggregate throughput of all the three FC
topologies. It may be appreciated that the switched fabric topology 492
provides the capability to interconnect large number of systems; to
sustain high bandwidth requirements; to match data rates between
connections of different speeds; and to match different cabling elements.
Reference numeral 491 denotes a loop topology known in the art as an
Arbitrated Loop ("AL"), operable with a connection standard referred to as
the FC-AL standard. The loop topology 491 interconnects a plurality of FC
devices or Nodes (denoted as loop ports or L.sub.-- Ports) such as, for
example, L.sub.-- Ports 420A through 420D, via unidirectional links, for
example, links 425A through 425D. Thus, this connection arrangement
enables each device to use the loop topology 491 as a point-to-point
connection between a sender and a receiver, irrespective of, any
intermediate devices disposed therebetween which merely act as "repeaters.
"
The arbitrated loop 491 provides a low-cost means of attaching multiple
devices without the need for hubs or switches. Although only four L.sub.--
Ports are shown in FIG. 4B, the loop provides shared bandwidth for up to
127 L.sub.-- Ports. Each L.sub.-- Port requests use of the loop when it
needs to communicate with another port; if the loop is free, the
requesting port sets up a bidirectional connection with the destination
port. The loop protocol permits an L.sub.-- Port to continuously arbitrate
to access the transmission medium to transmit to another L.sub.-- Port; a
fairness algorithm ensures that no L.sub.-- Port gets blocked from
accessing the loop. Once a connection is established, it can then deliver
any class of service appropriate to the traffic between the two L.sub.--
Ports.
As is known in the art, only one pair of L.sub.-- Ports may communicate at
one time. When these L.sub.-- Ports relinquish control of the loop,
another point-to-point connection between two L.sub.-- Ports may be
established. Further, the entire loop may be attached, in turn, to a FC
switch fabric port via what is known as an FL.sub.-- Port, or directly to
a single host system via an NL.sub.-- Port.
Because the presently preferred exemplary embodiment of the present
invention encompasses an FC-AL topology, such as the loop topology 491,
the general operation of this nodal configuration will be described in
greater detail hereinbelow.
It is known that the FC-AL standard allows each FC device to negotiate for
an Arbitrated Loop Physical Address (AL.sub.-- PA). Moreover, while
participating on an Arbitrated Loop, the FC devices must log in to each
other before commencing a loop transaction. If a device not logged in to
another device, it will discard any frames it receives from that device
until it is logged in. Since an initiator or driver must be able to manage
the target device with which it is communicating, the initiator keeps
track of an FC-specific identity triplet for that target device. This
FC-specific ID triplet comprises a target's Node.sub.-- Name, its
Port.sub.-- Name, and its AL.sub.-- PA. While the AL.sub.-- PA is
dynamically assigned upon a loop reset, the Node.sub.-- Name and
Port.sub.-- Name are formed from the device's unique World.sub.--
Wide.sub.-- Name.
When the devices come up onto an Arbitrated Loop upon a reset, they
configure their AL.sub.-- PAs in one of three ways: via a Soft Address
scheme, a Preferred Address scheme, or a Hard Address scheme. In a Soft
Address scheme, the device does not care what AL.sub.-- PA it is assigned.
Rather, it simply accepts the first free AL.sub.-- PA available.
In a Preferred Address scheme, the FC device would like to be assigned a
particular AL.sub.-- PA. However, if a desired AL.sub.-- PA is unavailable
for some reason, it will accept whichever AL.sub.-- PA that is free and
available. For example, after a device is assigned a specific AL.sub.-- PA
for the first time upon "global" system initialization following the
loading of the OS, that device will continue to request for that AL.sub.--
PA upon subsequent loop resets. However, once this device goes off-line
from the Arbitrated Loop, it will lose its ability to "prefer" that
AL.sub.-- PA and must resort to accepting the first free AL.sub.-- PA that
is available.
In a Hard Address scheme, the FC device can only operate at a particular
AL.sub.-- PA. According to the Loop Initialization Protocol ("LIP") in the
FC-AL Standard, which handles the configuration of the AL.sub.-- PAs, this
method of address configuration takes precedence over the first two
methods, namely, the Soft Address and Preferred Address schemes.
After all AL.sub.-- PA assignment issues have been resolved, the FC-devices
that act as initiators send out to all valid loop addresses a plurality of
what are known as Link Service Frames which comprise, among other things,
the LOGIN ("PLOGI") Frames, in order to discover what devices are on the
Arbitrated Loop. If a device accepts the LOGIN Frames from an initiator,
it will respond by transmitting in turn one or more ACKNOWLEDGMENT ("ACK")
Frames to the initiator. Then, responsive to these ACK Frames, a structure
in the initiator known as the Fibre Channel Manager ("FCMNGR") will
transmit a PROCESS LOGIN REQUEST ("PRLI") to the responding device which,
subsequently, identifies itself as being a target, an initiator, or both.
The information comprising a device's ID triplet and additional information
such as Device.sub.-- Type and Device.sub.-- Function (described below) is
typically passed to the FCMNGR in a driver or initiator via a LOG Function
that is a constituent element of the FC-AL standard. The information in
the LOG Function is mapped in accordance with the teachings of the present
invention to a link element pertaining to a higher-level OS-compatible
interface in order to provide for hot-plugging a device without a system
reboot or without having to incur some specialized software overhead to
"quieten" the loop.
Referring now to FIG. 5, therein is depicted an exemplary embodiment of the
mapping method in accordance with the teachings of the present invention,
wherein an FC-specific LOG Function information structure 530 is uniquely
mapped, via association means 599, to a link element 525 that is
interpretable by a higher-level OS-compatible interface standard. For
instance, in a SCSI environment, this link element 525 comprises a
BUS.sub.-- TARGET.sub.-- LUN nexus that has been previously described in
reference to FIG. 1. The information structure 530 relating to an FC
device preferably comprises its AL.sub.-- PA 535A, its unique Node.sub.--
Name 535B and Port.sub.-- Name 535C, Device.sub.-- Function 535D to
specify if it is an initiator, target, or both, and Device.sub.-- Type
535E to specify if the device is an array or a Direct Access Device
("DAD"), or the like. In accordance with the teachings of the present
invention, each link element associated with an information structure
relating to a specific FC device is preferably required to be unique
during the run time of the OS for a particular session.
It should be readily appreciated by those skilled in the art that by using
the teachings of the present invention, an Operating System need not know
that it is on a Fibre Channel Arbitrated Loop because the OS would use the
unique link element 525 in conjunction with association means 599 to send
upper-level commands to the FC devices. Furthermore, because of the
uniqueness of the mapping between the link element 525 and the FC
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