Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
METHOD AND SYSTEM FOR MAPPING ADDRESSING
OF SCSI DEVICES BETWEEN STORAGE AREA NETWORKS
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to data and information communication systems
and their
operation and, more particularly, to the field of storage area networking.
Even more particularly, the
present invention relates to fibre channel storage area networks ("SANS") and
to a method and system
for mapping addressing of SCSI devices between two SANs.
BACKGROUND OF THE INVENTION
Dramatic growth in the amount of data that must be stored, combined with the
need for faster,
more reliable and more efficient data access and data management capabilities,
have led many
organizations to seek an improved way of storing, accessing and managing data.
In traditional
computer networks, each storage device is connected to only one server, and
can be accessed only by
that server. The computer protocol used to connect and transfer data between
the server and storage
device is called the small computer system interface, or SCSI. As more data
must be stored and
retrieved, organizations increasingly are finding that this one-to-one, or
point-to-point, connection is
not sufficiently fast, efficient and reliable to support growing demands for
data access and storage. In
addition, in most organizations today, data back-up -- or creating a duplicate
copy of data to protect it
from corruption or loss -- is accomplished by moving large volumes of stored
data from a dedicated
storage device over the primary computer network to a back-up storage device.
Since the primary
computer network also is responsible for conducting day-to-day computer
operations, this added data
movement results in substantial congestion, slowing all other computer
operations.
Storage area networks, or SANS, which are computer networks dedicated to data
storage, can
help resolve some of these problems. A storage area network uses a different,
higher-performance
computer protocol, known as Fibre Channel, to transfer data. A storage area
network also removes
the one-to-one connection between servers and storage devices, and instead
allows many servers to
connect to and share access with many storage devices. The many-to-many
connection enabled by
the storage area network, combined with the Fibre Channel protocol, permits
faster, more efficient,
more reliable and more manageable data transfer processes. Furthermore, the
storage area network,
can be accomplished over data back-up operations, instead of over the primary
computer network,
thus substantially reducing congestion on the primary computer network and
allowing much more
efficient day-to-day operations.
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Most storage devices in the market, however, continue to be sold with the
small computer
system interface. Additionally, most organizations have made significant
investments in storage
devices and servers that use the small computer system interface. Therefore,
in order for devices of a
Fibre Channel storage area network to function with storage devices that use
SCSI, storage routers
must be installed between these devices. In particular, storage routers are
essential to shifting data
back-up processes from a primary computer network to the storage area network,
since most data
back-up storage devices use the SCSI interface and can only connect to the
storage area network
through a storage router. As new computer protocols are introduced, storage
routers will be
increasingly essential to enable rapid, seamless communication among servers,
storage devices and
storage area network devices that use diverse protocols.
However, typical SANS are local Fibre Channel networks that serve one
particular
organization or one particular site. These SANS can be quite large, but cannot
span great distances as
they have distance limitations imposed upon them by the infrastructure
necessary to carry Fibre
Channel. For example, the Fibre Channel standard defines a means to
communicate over spans up to
10 km and, in some cases, up to 30 km in length. In order to do this, however,
the organization
implementing the Fibre Channel network must typically own the fiber or lease
dark fiber from some
other party, which can be very expensive and, in most cases, is cost
prohibitive.
This is because the fibers used to carry Fibre Channel traffic can carry only
Fibre Channel
protocol traffic. They cannot be shared with other protocols. It is therefore
more cost effective to
transmit data over long distances using a protocol that can be carried over
already existing networks,
such as those owned by phone companies that can carry ATM traffic, SONET
traffic and IP traffic.
Therefore, SANs are usually limited as to the geographic area that they can
serve (i.e., they are
limited to local operation). Furthermore, two or more geographically diverse
SANs cannot inter-
connect in a seamless fashion such that they operate and behave as if they
were local to one another
because the infrastructure to connect them does not exist or is cost
prohibitive.
Related U.S. Patent Application entitled "Encapsulation Protocol for Linking
Storage Area
Networks Over a Packet Based Network" Serial No. 60/165,194, filed on November
12, 1999, (the
"Encapsulation" patent application) discloses an encapsulation protocol for
linking storage area
networks over a packet-based network that addresses the problems discussed
above. The
Encapsulation application is hereby incorporated by reference in its entirety.
However, even with the
solutions provided by the Encapsulation application, connecting two or more
SANs together using an
extender, such as the encapsulation protocol of the Encapsulation application,
requires the addresses
of SCSI devices from one SAN to be mapped to an intermediate address to get
across the extender,
and then to be mapped to another address on a remote SAN. This must be done in
order for initiators
(hosts) on one SAN to be able to address SCSI devices on a remote SAN as if
they were SCSI devices
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on the local SAN to which the initiator is attached. These mappings should be
done in a generic
fashion so that different types of architectures (i.e., parallel BUS, Fibre
Channel Protocol, etc.)
containing SCSI devices can all be mapped using the same method.
Some solutions do exist for mapping the addressing of SCSI devices between two
SANs, but
these typically attempt to propagate the entire address of a SCSI device
across the extender and re-use
the same address on the remote SAN. For example, a parallel BUS SCSI device on
a first SAN may
have an address of BUS:O, target:l, and LUN (logical unit identifier):0. In
prior art methods and
systems, the extender propagates this information from the first SAN to a
remote SAN, where the
same address is used to identify the device on the remote SAN. This approach,
however, has a
twofold problem. One, it uses a method of address mapping that is limited to a
single type of
architecture, i.e., the method only provides for mapping a single type of SCSI
architecture SCSI
device (e.g., parallel BUS SCSI devices). Two, because the device address must
be the same on both
sides of the extender, there is no means to dynamically map SCSI devices
across the extender.
SUMMARY OF THE INVENTION
Therefore, a need exists for a method and system for mapping addressing of
SCSI devices
between two SANs connected by a SAN extender (transport layer) that can map
SCSI device
addresses in a generic fashion such that SCSI device architecture can be
mapped using the same
method.
Still further, a need exists for a method and system for mapping addressing of
SCSI devices
between two SANS that can dynamically map SCSI device addresses across a SAN
extender.
The present invention provides a method and system for mapping addressing of
SCSI devices
between two SANs connected by a SAN extender over a packet-based network that
can substantially
eliminate or reduce the disadvantages and problems associated with use of a
fibre channel protocol
over large distances. In particular, the present invention provides a means
for seamlessly
interconnecting geographically distinct SANs, such that they operate as if
they were local to one
another by providing a means to generically and dynamically map SCSI device
addresses between
two SANS.
In particular, the present invention provides a method and system for
accessing a device from
a host, wherein the host and device are in separate SANs interconnected by a
transport layer, and
wherein the interface between the transport layer and the host SAN is a host
node and the interface
between the device SAN and the transport layer is a target node. The method of
this invention
comprises the steps of: at the target node, mapping the device address into a
Target, Generic
Identifier, and mapping the generic identifier into a transport identifier for
identifying the device on
the transport protocol; and, at the host node, mapping the device's transport
identifier into a host
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generic identifier, and mapping the host generic identifier into an address
accessible by the host. Each
node can be a fibre channel-to-SCSI router, such as those manufactured by
Crossroads Systems Inc.,
of Austin, Texas. The host generic identifier can comprise a mapping from the
target node transport
protocol address combined with the target generic identifier. The transport
layer can be a packet-
based network over which a SAN extender carries the FC protocol.
The present invention provides an important technical advantage of a method
and system for
mapping addressing of SCSI devices between two SANs connected by a SAN
extender that can map
SCSI device addresses in a generic fashion, such that any SCSI device
architecture can be mapped
using the same method.
Further still, the present invention provides an important technical advantage
of a method and
system for mapping addressing of SCSI devices between two SANS that can
dynamically map SCSI
device address across a SAN extender.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention and the advantages
thereof may be
acquired by referring to the following description, taken in conjunction with
the accompanying
drawings in which like reference numbers indicate like features and wherein:
FIGURE 1 is a simplified block diagram illustrating one implementation of the
method and
system of this invention within a typical SAN environment.
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention are illustrated in the FIGURES,
like numerals
being used to refer to like and corresponding parts of various drawings.
The present invention provides a method and system for mapping addressing of
SCSI devices
between two SANs connected by a SAN extender across a packet-based network
that take advantage
of existing telecommunication networks to efficiently and cost-effectively
connect multiple, and
perhaps geographically diverse, SANs such that they can operate as if they
were a single storage area
network. Host devices on one SAN can therefore access target devices on a
remote SAN as if the two
were part of a single SAN. The method and system of this invention can thus
effectively overcome
the distance limitations of existing fibre channel networks so that the SAN
model can be extended to
many SANs over many miles. The present invention could, for example, be used
to link a corporate
SAN in Los Angeles to another corporate SAN in New York City or Tokyo. In the
case of storage
recovery, this invention will allow a backup library to reside off site at a
remote location, thus
ensuring data integrity should the local location be damaged by disaster, like
fire or flood. SANS
implementing the present invention thus need not be limited to local use only.
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To connect local SANS over greater distances than allowed under the fibre
channel protocol,
the present invention can work together with the SAN extender disclosed in the
Encapsulation
application. The Encapsulation application defines an encapsulation protocol
("EP") that runs the
Fibre channel protocol in such a way that it can travel over any packet-based
transport, such as an
asynchronous transfer mode ("ATM") or Ethernet network. Together with the
extender disclosed in
the Encapsulation application, the current invention provides a mechanism for
generically mapping
the addressing of SCSI devices on a SAN to one or more remote SANs, across any
transport layer that
is used to connect the SANS (e.g., ATM, gigabit Ethernet, or Fibre Channel).
A node (Fibre Channel-to-SCSI muter) is used to connect each SAN to the
extender transport
maintains two mapping tables, as discussed more fully below, to map device
addresses across the
transport protocol to another node. The nature of the tables maintained by a
node depends on whether
the node is a host node, or a target node. This distribution is described more
fully below.
The nodes at either end of the extender transport connecting any two SANS
build their
mapping tables slightly differently, depending on whether they are the target
node or the host
1 S (initiator) node. A target node (to which target devices are attached)
builds tables to map a SCSI
device addresses into first a target generic identifier, and then to a
transport identifier an (address) that
is used on the extender transport protocol. An initiator node (the node to
which hosts seeking to
access a target device are attached) builds tables to map the address received
from the extender
protocol (the transport identifier) back into a valid SCSI device address
based on the current
architecture (e.g., parallel BUS, fibre channel, etc.) This method is
explained more fully below.
According to the teachings of this invention, a target node first maps a SCSI
device address to
a target generic identifier on the target node. This target generic identifier
can then be mapped into a
transport identifier that is used as a device identifier on the extender
transport. The target generic
identifier and the transport identifier can, in some, instances, be the same.
The target node informs
the initiator node of the device transport identifier and also of the address
of the target node on the
extender transport. The initiator node is thus provided with the information
needed to determine the
target node that owns the SCSI device and also with the device transport
identifier for the particular
device. The initiator node can then map the target node address and device
transport identifier to a
host generic identifier on the initiator node, and then maps the host generic
identifier to an address
that can be presented to initiators on the local initiator SAN.
FIGURE 1 is a simplified block diagram illustrating one implementation of the
method and
system of this invention within a typical SAN environment. Network 100 of
FIGURE 1 includes #1
host SAN 110 and #2 host SAN 112, which can be local fibre channel SANS. #1
host SAN 110 and
#2 host SAN 112 can access target SAN 115, which can also be a local fibre
channel SAN for, for
example, tape backup and disk mirroring. #1 host SAN 110 is communicatively
connected to #1
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initiator node 120, and #2 host SAN 112 is communicatively connected to #2
initiator node 130.
Target SAN 115 is communicatively connected to target node 150. #1 initiator
node 120, #2 initiator
node 130, and target node 150 can be fibre channel-to-SCSI routers, such as
those manufactured and
sold by Crossroads Systems Inc. of Austin, Texas. Nodes 120, 130 and 150 can
be interfaces to the
rest of the network 100 for SANS 110, 112 and 115.
The Fiber channel-to-SCSI routers that nodes 120, 130 and 150 comprise can all
implement
the EP layer (as disclosed in the Encapsulation application) such that the
fibre channel protocol flows
seamlessly over the packet-based WAN (wide area network) 140. WAN 140
represents a physical
packet-based transport, such as ATM or Ethernet. WAN 140 can be a dedicated
link or switched
network. SANs 110, 112 and 115 are connected to their respective nodes via
fibre channel links 190.
Nodes 120, 130 and 150 can each be connected to WAN 140 via network links 192.
Fibre channel
links 190 can be copper, Fibre optic links, or any other such network link as
known to these familiar
with the art, as required for a given application. Network links 192 can
similarly be any such network
link, as needed.
#1 host SAN 110, #2 host SAN 112, and target SAN 115 can comprise multiple
initiators and
multiple targets, respectively. For example, target SAN 115 includes fibre
channel hub (switch) 160,
tape library 170, and disk 180. Although only tape library 170 and disk 180
are shown, multiple
initiators and target devices can be attached to fibre channel hub 160 and
through it to fibre
channel-to-SCSI router (target node) 150. Target SAN 115 can thus comprise
multiple hosts and
multiple initiators.
The method and system of the present invention require an extender protocol to
connect the
two or more SANs between which target addresses will be mapped.
The Encapsulation Application discloses such an extender protocol (EP). The
method and
system for mapping SCSI addresses of the present invention uses this
encapsulation protocol to
provide a transport on which to carry the mapping used to allow initiators on
one SAN to address
SCSI devices on a remote SAN as if they were SCSI devices on the local SAN to
which the initiator
is attached. Devices on a remote SAN thus can be represented in such a way
that they are made
available to initiators on other SANS. The Encapsulation Application discloses
a compatible
encapsulation protocol that can be used with the present invention.
FIGURE 1 illustrates how the method and system of this invention can be used
to map SCSI
device addresses between Fibre channel SANS interconnected over a network
protocol, such as an
ATM network. The example of FIGURE 1 is used for illustrative purposes only,
and does not
preclude using the method and system of this invention for mapping other SCSI
architecture device
addresses or using a different protocol to interconnect the SANs.
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To accomplish the mapping of the method and system of this invention, target
node 150 will
build two tables. The first table maps the address information for each SCSI
device attached to target
node 150 into a unique target generic identifier for each SCSI device. For
example, if tape library 170
and disk 180 have FC addresses 0 x 1 and 0 x 2 , respectively, and tape
library 170 has two logical
unit identifiers (LUNs) of 0 and 1, and disk 180 has a single LUN of 0, then
the following table is
created by target node 150 to map the SCSI device addresses to target generic
identifiers.
TABLE 1
Tar et Generic IdentifierFC Device AddressLUN Identifier
0 0x1 0
1 Oxl 1
2 0x2 0
Target node 150 uses the target generic identifiers to map each device address
into a transport
identifier that can then be used to identify the device on the extender
transport protocol. In this
example, the device transport identifier on the extender transport protocol is
the same as the generic
identifier. However, this need not be the case, as other identifiers could
instead be used. Table 2
below shows the mapping of target generic identifier to device transport
identifier.
TABLE 2
Target Generic Transport Identifier
Identifier
0 0
1 1
2 2
Once Tables 1 and 2 are created, target node 150 can inform #1 initiator node
120 and #2
initiator node 130 of the target devices it has made available and their
respective transport identifiers.
The method for notifying other nodes in the network can be any method as known
to those familiar in
the art.
#1 initiator node 120 and #2 initiator node 130 each similarly build two
tables. The first table
that each initiator node creates is used to map the target node's transport
protocol address and each
device transport identifier generated by target node 150 into a host initiator
generic identifier within
the local node. The host generic identifier associated with a given target
device represents a
combination of the target node transport protocol address and the devices
transport identifier.
Assuming for this example that target node 150 has an ATM address of
0x01020304, then the
following Table 3 would be created in #1 initiator node 120 and #2 initiator
node 130.
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TABLE 3
Host Generic Target Node Transport
Identifier Transport Address Identifier
0 (Tape) 0x01020304 0 (Tape)
1 (Tape) 0x01020304 1 (Tape)
2 (Disk) 0x01020304 2 (Disk)
In this example, all devices attached to target node 150 are made available to
#1 initiator node
120 and #2 initiator node 130. However, a target node, such as target node
150, may decide to make
only selected devices accessible to initiator nodes by leaving selected SCSI
device addresses out of
the tables it generates for the mapping. Such different mapping configurations
are intended to be
within the scope of this invention. Any combination of such mappings is
contemplated by this
invention.
#1 initiator node 120 and #2 initiator node 130 also build a table, such as
Tables 4 and 5
below, that map the host generic identifier into a form that can be used by
hosts on the local SAN to
address the target devices. In the examples shown below in Tables 4 and 5, the
host generic
identifiers are mapped into LUNs on a single fibre channel target. This fibre
channel target is a
simulated target within the host SAN that is sued to represent the remote
target devices on target SAN
115 so that local hosts can access each device.
TABLE 4
FC LUN (Initiator SAN Host Generic Identifier
on target)
0 1 (Tape)
1 0 (Tape)
2 2 (Disk)
TABLE 5
FCLUN Host Generic Identifier
0 2 (Disk)
The method and system of this invention can thus use a simulated target at a
host SAN, onto
which the can map the addresses of one or more real target devices located at
a remote target SAN.
The simulated fibre channel target to which the host generic identifiers) are
mapped can then be used
to access the remote target device as if the remote targets) were located
within the local SAN.
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The method and system of this invention do not preclude other mappings from
occurring, i.e.,
each host generic identifier could instead be mapped to a unique simulated
fibre channel target within
the local host SAN. Any combination of such mappings can be used and is within
the scope of this
invention. In fact, initiator nodes may decide to map only selected target
devices or to map all target
devices. Target devices can also be mapped in any order. For example, in Table
4 above, #1 initiator
node 120 has mapped all of the target devices from target SAN 115 into a
simulated fibre channel
target, but in a different order. Host generic identifier 1 is mapped to Fibre
Channel LUN 0, host
generic identifier 0 is mapped to Fibre Channel LUN 1, and host generic
identifier 2 is mapped to
Fibre Channel LUN 2. Any such combination is within the scope of this
invention. By contrast, #2
initiator node 130 in this example maps only one target device, associated
with host generic identifier
2, into a Fibre Channel LUN 0.
By using these mapping tables, initiators on local SANS connected to # 1
initiator node 120
and #2 initiator node 130 can access the SCSI target devices on target SAN 115
connected to target
node 150. According to the teachings of this invention, all such remote target
devices, or a limited
number of such devices, can be made accessible to remote initiator SANs from a
local target SAN.
The present invention thus allows any type of SCSI target device to be
accessed across any type of
extender protocol by mapping the device addresses in a generic fashion. In
addition, the method and
system of this invention provide the capability to access all such target
devices, or only a limited
number of such target devices, on a target SAN from one or more remote
initiator SANS, depending
on the mapping tables created. The present invention also allows multiple SANS
of different
architectures and protocols to be interconnected in a generic fashion.
The method and system of this invention can be implemented within a fibre
channel-to-SCSI
router, such as routers 120, 130 and 150 of FIGURE 1 (nodes 120, 130 and 150).
The present
invention can be implemented purely as computer executable software
instructions stored in memory
within the fibre channel-to-SCSI routers, and can be easily upgraded as new
versions with new
functionality are created. No change in the hardware of existing fibre channel-
to-SCSI routers is
required to incorporate this invention. The memory in which the software
instructions of this
invention can be stored can be RAM (random access memory) or ROM (read-only
memory) or other
such memory storage devices.
The method and system of this invention can be used with any compatible
encapsulation
protocol, such as that disclosed in the Encapsulation Application, and can be
used over existing
Internet infrastructures and other existing network protocols. For example,
the extension protocol can
be a typical IP network protocol, an ATM network, gigabit Ethernet, or any
protocol that allows data
packets to flow between nodes. The method and system of this invention allows
for mapping of SCSI
device addresses between any SCSI protocol SANS on either end of an extension
network.
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The present invention is not limited to use in applications having storage
area networks that
each use the same fibre channel protocol. For example, target host 115 and
initiator hosts 110 and
112 of FIGURE 1 can each use a different protocol and the method and system
for mapping SCSI
target device addresses of this invention can continue to function as
disclosed herein. However, a
compatible encapsulation protocol is required.
The present invention provides the capability for extending a SAN model to
many SANS over
distances much greater than those currently allowed by the fibre channel
protocol. This invention
provides the capability to interconnect SANs in geographically diverse
locations, such as different
cities, in such a way that they can function in a seamless manner as if they
comprise a single local
10 SAN. Further, for storage recovery purposes, the present invention allows a
backup library to reside
off site at a remote location, thus ensuring data integrity should the local
location be damaged by
some failure or disaster.
Although the present invention has been described in detail herein with
reference to the
illustrative embodiments, it should be understood that the description is by
way of example only and
is not to be construed in a limiting sense. It is to be further understood,
therefore, that numerous
changes in the details of the embodiments of this invention and additional
embodiments of this
invention will be apparent to, and may be made by, persons of ordinary skill
in the art having
reference to this description. It is contemplated that all such changes and
additional embodiments are
within the spirit and true scope of this invention as claimed below.
