Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
2001-01-24
2002-05-21
Kim, Hong (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S113000, C707S793000, C714S006130
Reexamination Certificate
active
06393538
ABSTRACT:
TECHNICAL FIELD
There is a case where when a storage medium (primary site) that is the main becomes unusable in a file system handling user data due to, for example, occurrence of disaster, it is required to promptly switch it to another system to resume the operation without losing the user data written in the primary site up to the time of the occurrence of disaster. In order to duplicate data of a primary file unit to prevent the loss of the data, it is necessary to prepare a secondary file unit, and update data in the two file units in any technique when the data is updated.
The present invention relates to a remote transfer method for transferring update data (write data) from the primary file unit to the secondary file unit, when a host apparatus performs data-update (writing) in the primary file unit, so as to perform data-update in the secondary file unit which is same as the data-update performed in the primary file unit.
BACKGROUND ART
There are generally two techniques for duplicating data.
One is that a host apparatus
1
simultaneously performs writing in two file units
2
A and
2
B to realize duplicating of data, as shown in FIG.
8
. In such technique, it is possible to ensure equivalence of the data in the two file units
2
A and
2
B.
The other is a technique in which file units (FCUs)
2
C and
2
D are communicably connected, and when the host apparatus
1
updates (writes) data in one file unit (primary file unit)
2
C, the update data (write data) is transferred from the primary file unit
2
C to the secondary file unit
2
D, thereby to realize duplicating of the data, as shown in FIG.
9
. In this technique, it is possible to ensure equivalence of the data in the two file units
2
C and
2
D, as well.
Incidentally, data transfer from the primary file unit
2
C to the secondary file unit
2
D as above is called remote transfer. The file unit is sometimes called a file control unit (FCU: File Control Unit).
In the former technique, the host apparatus
1
simultaneously writes in the two file units
2
A and
2
B, so that the file units
2
A and
2
B can realize duplicating of the data without performing any special process. On the other hand, in the latter manner, the primary file unit
2
C transfers data to the secondary file unit
2
D, whereby the host apparatus
1
can realize duplicating of the data only by performing usual data-writing, being conscious of only one storage apparatus (primary file unit
2
C), without performing any special process.
In the host apparatus
1
, processes for its primary operations are performed, which is naturally a large load thereon. When the host apparatus
1
performs writing data into the secondary file unit
2
D in the former technique, a further load is applied to the host apparatus
1
, which is undesirable. Namely, in the former technique, since the host apparatus
1
simultaneously performs writing data into the two file units
2
A and
2
B, the host apparatus
1
is required to operate while being always conscious of duplicating of the data, and to perform a special interface process or the like.
For this reason, the latter technique is employed in these years. Wherein, it is general that the host apparatus
1
performs updating data in only the primary file unit
2
C, assigning the primary file unit
2
C to transfer the data to the secondary file unit
2
D to duplicate the data. In this case, the host apparatus
1
is not required to perform any special process for duplicating the data, but required to perform only usual data-update in one file unit
2
C. The primary file unit
2
C therefore functions as an upper apparatus of the secondary file unit
2
D to transfer/update the data to/in the secondary file unit
2
D, whereby the data is duplicated.
Detailed structures of the system, and the files units
2
C and
2
D used in the system applied the latter technique will be described next with reference to FIG.
10
.
As shown in
FIG. 10
, the primary file unit
1
C and the secondary file unit
2
D have the same structure, each of which comprises a CA (Channel Adapter)
11
, an RM (Resource Manager)
12
, a TS (Table Storage)
13
, an RA (Remote Adapter)
14
, a CFR (Cache Function Engine)
15
, a cache memory
16
, a DA (Device Adapter)
17
, a command bus
18
, a data bus
19
, and a physical device
20
.
The CA
11
is a module in charge of an interface control with the host apparatus
1
via an interface
21
. The RM
12
is a module in charge of resource management with respect to a basic operation. The TS
13
is a memory used as a table for the resource management.
The RA
14
is a module in charge of transmission/reception of data to/from the file unit
2
C or
2
D via an interface
22
. The CFE
15
is a module in charge of management of the cache memory
16
. The DA
17
is a module in charge of an interface control with the physical device
20
that is a magnetic disk apparatus
20
a.
Incidentally, the cache memory
16
is provided with an inter-module communication area
16
a.
The communication area
16
a
is served to temporarily store data that is to be transmitted/received among the modules
11
,
14
and
17
of each of the file units
2
C and
2
D.
The command bus
18
is served to exchange commands among the CA
11
, the RM
12
, the RA
14
, the CFE
15
and the DA
17
. The data bus
19
is served to exchange data among the CA
11
, the RA
14
, the CFE
15
, the cache memory
16
and the DA
17
.
FIG. 10
depicts a case where the host apparatus
1
has two channels
1
a,
and each of the file units
2
C and
2
D has two CAs
11
, two RAs
14
, four DAs
17
, and four magnetic disk apparatuses
20
a
as the physical device
20
.
The primary file unit
2
C is connected to the host apparatus
1
via the interface
21
, while the secondary file unit
2
D is connected to the primary file unit
2
C via the interface
22
. The interface
21
connects the channel
1
a
of the host apparatus
1
to the CA
11
of the primary file unit
2
C. The interface
22
connects the RA
14
of the primary file unit
2
C to the RA
14
of the secondary file unit
2
D.
As these interfaces
21
and
11
, same device, that is, ESCON interface, for example, are used. The primary unit
2
C has a function enabling an access from the RA
14
thereof t the RA
14
of the secondary file unit
2
D in the similar sequence to that to the channel. In other words, the RA
14
of the primary file unit
2
C is such configured as to be able to issue a command to the RA
14
of the secondary file unit
2
D in the similar sequence to that performed between the channel of the host apparatus
1
and the CA
11
of the primary file unit
2
C.
Incidentally, hardware of the CA
11
and hardware of the RA
14
are basically the same. The RA
14
of the primary file unit
2
C operates equivalent to the channel, as described above. Therefore, it is unnecessary to provide, as the RA
14
of the secondary file unit
2
D, an adapter having a special function, because an adapter having a function as the CA
11
connected to the ordinary channel
1
a
is sufficient.
When the host apparatus
1
writes data into the primary file unit
2
C, the data is transferred in units of record to the primary file unit
2
C, and temporarily written into the cache memory
16
. When data for one track of the magnetic disk apparatus
20
a,
which is an object to be written, is written into the cache memory
16
of the primary file unit
2
C, remote transfer to the secondary file unit
2
D is carried out, then data-writing to the magnetic disk apparatus
20
a
of the primary file unit
2
C is carried out.
FIG. 11
is a diagram showing an example of structure of data for one track to be temporarily written in the cache memory
16
of the primary file unit
2
C in order to transfer the data to the secondary file unit
2
D and write the same into the physical device
20
. As shown in
FIG. 11
, the data for one track sent to the secondary file unit
2
D is made up of a control information field on the head end and a plurality (N in
FIG. 11
) of record fields.
In th
Fujitsu Limited
Kim Hong
Staas & Halsey , LLP
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