Electrical computers and digital processing systems: support – Digital data processing system initialization or configuration
Reexamination Certificate
1998-12-14
2001-05-29
Heckler, Thomas M. (Department: 2182)
Electrical computers and digital processing systems: support
Digital data processing system initialization or configuration
C713S100000
Reexamination Certificate
active
06240511
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method and apparatus for detecting changes in a configuration of a computer system.
DESCRIPTION OF THE RELATED ART
Many computer systems include one or more host computers and one or more system resources that are accessible thereby. An example of such a computer system is shown in
FIG. 1
, and includes a host computer
1
and a storage system
3
that serves as a system resource accessible by the host computer
1
. The storage system
3
includes a plurality of storage devices on which data are stored. In the exemplary system shown in
FIG. 1
, the storage system
3
includes a plurality of disk drives
5
a
and
5
b
and a plurality of disk controllers
7
a
-
7
b
that respectively control access to the disk drives
5
a
and
5
b
. The storage system
3
further includes a plurality of storage bus directors
9
a-d
that control communication with the host computer
1
over communication buses
17
a-d
. Communications buses
17
a-d
interface to the storage system
3
through ports
18
a-d
. Finally, the storage system
3
includes an internal bus
13
over which the storage bus directors
9
a-d
and the disk controllers
7
a
-
7
b
communicate.
The host computer
1
includes a processor
16
and one or more host bus adapters
15
a-d
that each controls communication between the processor
16
and the storage system
3
via a corresponding one of the communication buses
17
a-d
. It should be appreciated that rather than a single processor
16
, the host computer
1
can include multiple processors. Each of the buses
17
a-d
can be any of a number of different types of communication links, with each of the host bus adapters
15
a-d
and the storage bus directors
9
a-d
being adapted to communicate using an appropriate protocol for the communication bus coupled between them. For example, each of the communication buses
17
a-d
can be implemented as a SCSI bus, with the directors
9
a-d
and adapters
15
a-d
each being a SCSI driver. Alternatively, communication between the host computer
1
and the storage system
3
can be performed over a Fibre Channel fabric, where the buses
17
a-d
are Fibre Channel links.
As shown in the exemplary system of
FIG. 1
, some computer systems employ multiple paths for communicating between the host computer
1
and the storage system
3
(e.g., each path includes one of the host bus adapters
15
a-d
, one of the buses
17
a-d
, one of the ports
18
a-d
, and one of the storage bus directors
9
a-d
in FIG.
1
). In some such systems, each of the host bus adapters
15
a-d
has the ability to access each of the disk drives
5
a-b
, through an appropriate storage bus director and disk controller.
FIG. 2
is a schematic representation of a number of mapping layers that may exist in a computer system such as the one shown in FIG.
1
. The mapping layers include an application layer
21
which includes application programs executing on the processor
16
of the host computer
1
. The application layer
21
will generally refer to data objects used thereby with a label or identifier such as a file name, and will have no knowledge about where the corresponding file is physically stored on the storage system
3
(FIG.
1
). In addition, the host computer
1
also includes a file system and/or logical volume manager (LVM) layer
23
that maps each data object specified by the application layer
21
to a particular logical volume (that the host computer
1
perceives to correspond to an actual physical storage device) wherein the data object is stored. The file system/LVM layer
23
will generally refer to a logical volume (also referred herein as a “raw storage device”) using a label or identifier that is at least partially descriptive of a physical component of the computer system that is used by the host computer
1
when accessing the logical volume. The physically descriptive information may include, for example, information descriptive of the one of the multiple paths via which the logical volume may be accessed, as well as a unique identifier for the raw storage device. For example, for a SCSI connection, the device identifier “/dev/dsk/c
0
t
0
d
0
” may be used to refer to a raw storage device or logical volume accessible at a channel zero (c
0
) (which can be any of the multiple paths in FIG.
1
), and having a target number zero (t
0
) and a logical unit number (LUN) zero (d
0
) that together uniquely identify the raw storage device.
Below the file system/LVM layer
23
is a multi-path mapping layer
25
that maps the logical volume address specified by the file system/LVM layer
23
, through a particular one of the multiple system paths, to the logical volume address to be presented to the storage system
3
. Thus, the multi-path mapping layer
25
not only specifies a particular logical volume address, but also specifies a particular one of the multiple system paths used to access the specified logical volume.
If the storage system
3
were not an intelligent storage system, the logical volume address specified by the multi-pathing layer
25
would identify a particular raw physical device (e.g., one of the disk drives
5
a-b
) within the storage system
3
. However, in an intelligent storage system such as that shown in
FIG. 1
, the storage system itself may include a further mapping layer
27
, such that the logical volume address passed from the host computer
1
may not correspond directly to an actual physical device (e.g., a disk drive
5
a-b
) in the storage system
3
. Rather, a logical volume specified by the host computer
1
can be spread across multiple physical storage devices (e.g., disk drives
5
a-b
) or multiple logical volumes accessed by the host computer
1
can be stored on a single physical storage device.
As discussed above, application programs running in the application layer
21
typically access logical volumes within the storage system
3
via the file system/LVM layer
23
, which uses device identifiers for the logical volumes that include information descriptive of a physical component of the computer system through which the logical volumes are accessed. This can cause problems when changes are made to the physical configuration of the computer system. User flexibility in reconfiguring a computer system has become more and more prevalent with the advent of Fibre Channel. Fibre Channel is a communication protocol that enables computer system components that were previously incapable of communicating to be coupled together in a manner that enables communication therebetween. For example, using Fibre Channel a first computer system resource that communicates using SCSI can communicate with a second computer system resource that communicates using Ethernet. An example of a computer system implemented using Fibre Channel is shown in
FIG. 4
, wherein a host computer
1
is coupled to a storage system
3
via a Fibre Channel cloud
100
. It should be appreciated that the Fibre Channel cloud
100
can include a number of switching and hub components, such that the host computer
1
and the storage system
3
can communicate with other system components via the cloud
100
.
It should be appreciated that when the computer system of
FIG. 4
is brought on line, the host computer
1
will be booted or initialized, and will go through a process of assigning device identifiers (e.g., “/dev/dsk/c
0
t
0
d
0
” as discussed above), to each raw storage device or logical volume accessible to the host computer through the Fibre Channel cloud
100
. It should be appreciated that the assignment of a particular one of the communication paths
102
a-d
as channel c
0
is fairly arbitrary, and is not initially significant, so long as each of the paths
102
a-d
is assigned a unique channel number. Referring to the illustrative example shown in
FIG. 4
, during initialization, the communication path
102
a
initially may be assigned channel designation c
0
and communication path
102
b
initially may be assigned channel designation c
1
. A first logical volume
104
Blumenau Steven M.
Cohen Steven
Madden, Jr. John F.
EMC Corporation
Heckler Thomas M.
Wolf Greenfield & Sacks P.C.
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