Data sharing method and system between information...

Details Data sharing method and system between information... Data sharing method and system between information...

2000-01-05

2003-02-04

Kim, Hong (Department: 2187)

Electrical computers and digital processing systems: memory

Storage accessing and control

Specific memory composition

C711S147000, C360S048000

Reexamination Certificate

active

06516385

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to a data sharing method and system between information processing systems, and more particularly to a data access method and apparatus for use in a computer system comprising an information processing system and another information processing system having an internal auxiliary storage device connected thereto for accessing the internal auxiliary storage device from any information processing system.
A general-purpose large computer (or a main frame which is hereinafter referred to as the “information processing system”) typically employs variable length block format magnetic disk units as external storage devices. To access such a magnetic disk unit, a variable length access interface (for example, CKD (Count Key Data)) is employed for enabling data accesses in variable length block format. Conventionally, variable-length block formatted data have been physically implemented on a disk unit having this variable length access interface. In recent years, however, disk arrays composed of relatively inexpensive disk units generally used for PC and workstations have been widespread as storage devices for variable-length block formatted data.
In regard to a disk array for use with a general-purpose information processing system, disk units conforming to a fixed length block format referred to as FBA (Fixed Block Architecture) are typically used for individual disk units, as-found in a literature “Main Frame '98,” published by Nikkei BP, pp. 126-130. Then, an associated disk array controller has a fixed length/variable length block format conversion function, so that an information processing system is connected to the disk controller through a variable length access interface, for example, a SCSI (Small Computer Interface) interface. A read/write request from an information processing system, such as that issued from an operating system, is composed of a plurality of input/output commands referred to as CCWs (Channel Command Words). The plurality of CCWs are referred to as a “CCW chain.” The CCW chain is created by the operating system of the information processing system in accordance with a request from an application program.
A magnetic disk drive is typically utilized as a disk subsystem comprising a disk control unit and disk units, which is mounted external to an information processing system. When the information processing system reads/writes data from/into a disk unit, the information processing system first sends a command conforming to a variable length block format to the disk subsystem. The disk control unit disposed in the disk subsystem receives the command issued by the information processing system, and converts the command from the variable length block format to a fixed length block format such that the disk unit can be accessed by this command (disclosed in JP-A-6-150557).
FIG. 2
illustrates an information processing system which has an external disk subsystem connected thereto. The information processing system
3
is connected to the disk subsystem
4
through a communication line
34
. The information processing system
3
is provided with a plurality of I/O channels
33
for controlling transmission/reception of information to/from external devices in place of the information processing system
3
. One of the I/O channels
33
is connected to the disk subsystem
4
which comprises a disk controller
41
and a plurality of fixed length block format disk units
42
operating under the control of the disk controller
41
. A variable length access interface is included in the disk controller
41
. The I/O channels
33
constitute a variable length access interface. The disk controller
41
has a function of performing conversion between the variable length block format and the fixed length block format. Each of the disk units
42
is accessed through a fixed length access interface.
Now, a conventional method of accessing data from the information processing system to the disk subsystem will be described in connection with data read/write operations with reference to a flow chart of FIG.
6
.
Step
601
: For accessing data stored in a disk unit
42
, a CPU
32
creates a read/write request as a CCW for controlling the data and the disk unit through an operating system running on the CPU
32
, and stores the read/write request in a main memory
31
. The CPU
32
initiates the associated I/O channel
33
to start the read/write request. After this processing, the CPU
32
is released for performing other processing.
Step
602
: The I/O channel
33
issues the read/write access to the disk controller
41
to initiate the disk unit
42
.
Step
603
: The I/O channel
33
regards the plurality of disk control units
42
under the control of the disk control unit
41
as conforming to a variable length block format based on a count-key-data (CKD) architecture, and issues the variable-length formatted CCW residing on the main memory
31
to the disk controller
41
.
Step
604
: The disk controller
41
converts the variable-length block formatted CCW to a fixed length block formatted counterpart, i.e., a SCSI command.
Step
605
: After converting the CCW to the SCSI command, the disk controller
41
sends the command to the plurality of subordinate disk units
42
for controlling them to perform a seek operation to position their respective heads over target records. For a data read, requested data is read from the disk unit
42
, transferred through the disk controller
41
and the I/O channel
33
, and written into the main memory
31
. For a data write, data on the main memory
31
is read, and a write request is issued to the disk controller
41
.
Step
606
: When the data transfer is completed, the I/O channel
33
generates an interrupt to the CPU
32
to inform the same of the completion of the data transfer, thus terminating the I/O operation.
The sequence of I/O operations mentioned above is described in “M-series Processing System (M/ASA Mode) Manual” (document number 8080-2-146) published by Hitachi Ltd. and “H-6582-C3 Model Disk Control Unit Manual” (document number 8080-2-130-60) also published by Hitachi Ltd.
A prior art internal disk is described, for example, in “Main Frame '98” published by Nikkei BP, pp. 53-54. This literature discloses a technique for installing a fixed length block format disk within a chassis of an information processing system. Specifically, a fixed length block format disk is directly connected to a processor within the information processing system, such that the processor interprets a CCW chain generated by an operating system, referred to as “SAP” (System Assist Processor), residing on another processor in the information processing system, accesses the fixed length block format disk, performs fixed length/variable length block format conversion, and executes an input/output request. The fixed length/variable length block format conversion is implemented by using a portion of a main memory as a disk cache. Since this technique permits the utilization of the small disk built in the chassis of the information processing system without the need for modifying the existing operating system or application programs, a consequent reduction in size and cost can be accomplished for the information processing system.
In the disclosed technique mentioned above, however, connected to the processor of the information processing system through the interface conforming to the fixed length block format is only the fixed length disk unit built in the chassis. No such interface conforming to the fixed length block format is provided for any storage external to the chassis, i.e., storage shared by other hosts such as other information processing systems.
FIG. 3
illustrates an example of an information processing system
301
which has a prior art internal disk unit. In conjunction with the system of
FIG. 3
, a method of processing a read/write request, when sent from the information processing system
301
, will be described with reference to a flow chart of FIG.
4

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