Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
1996-12-30
2001-09-18
Kim, Matthew (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C370S294000, C370S543000, C370S544000, C710S052000, C710S001000, C711S114000
Reexamination Certificate
active
06292875
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a storage device having a plurality of storage parts such as magnetic disk drives, and a method of accessing such a storage device.
A storage device is known in which a plurality of different kinds of data streams are written, in dispersed formation, into storage parts such as magnetic disk drives every unit data and is sequentially read therefrom every unit data. Such a storage device enables a multiple access, and may be applied to various applications such as a VOD (Video On Demand). It is desired to realize a flexibility of access to the storage device having a plurality of storage parts.
2. Description of the Related Art
FIG. 1
is a block diagram of a conventional storage device having seven magnetic disk drives DSK
1
through DSK
7
respectively serving as storage parts. Symbols “title
1
-
1
”, “title
1
-
2
”, “title
1
-
3
”, . . . respectively denote unit data, which is obtained by dividing a data stream title
1
. Symbols “title
2
-
1
”, “title
2
-
2
”, “title
2
-
3
”, . . . respectively denote unit data, which is obtained by dividing a data stream title
2
. Similarly, Symbols “title
7
-
1
”, “title
7
-
2
”, “title
7
-
3
”, . . . respectively denote unit data, which is obtained by dividing a data stream title
7
. The pieces of the data stream title
1
-title
7
are stored, every unit data, in the magnetic disk devices DSK
1
-DSK
7
in the dispersed formation. A storage method as described above is called a striping method.
When the data stream title
1
is specified and read, the unit data title
1
-
1
is read from the magnetic disk drive DSK
1
. Next, the unit data title
1
-
2
is read from the magnetic disk drive DSK
2
. Then, the unit data title
1
-
3
is read from the magnetic disk drive DSK
3
. The above read operation is indicated by arrows of broken lines shown in FIG.
1
. That is, the magnetic disk drives are sequentially accessed in the order of DSK
1
, DSK
2
, DSK
3
, DSK
4
, DSK
5
, DSK
6
, DSK
7
, DSK
1
, . . . , whereby the data stream title
1
is read therefrom. When the data title
6
is specified and read, the magnetic disk drives DSK
1
through DSK
7
are accessed in the order of DSK
6
, DSK
7
, DSK
1
, DSK
2
, DSK
3
, DSK
4
, DSK
6
, DSK
6
, DSK
7
, . . . , so that the reading cycles thereof do not conflict with the cycles for reading the unit data title
1
-
6
, title
1
-
7
, . . .
For example, if the data stream is video data, the unit data is defined by compressing and encoding video data equal to one frame or a few frames. If the title title
2
is specified, the first unit data is read from the magnetic disk drive DSK
2
as title
2
-
1
, and the next unit data is read from the magnetic disk drive DSK
3
as title
2
-
2
. On the receiving and reproducing side, the unit data is decoded and buffered, so that the consecutive data stream can be reproduced. The compressing and encoding method for video data may be various known methods. For example, a standardized compressing and encoding method such as an MPEG (Moving Picture Experts Group) can be used. In this case, the video data is stored in the dispersed formation every unit data equal to one frame or a few frames.
FIG. 2
is a sequence diagram of a read operation, which was proposed in a prior Japanese Patent Application which is not laid-opened or published and is not prior art.
In
FIG. 2
, symbols (DSK
1
)-(DSKn) indicate access states of the magnetic disk drives DSK
1
-DSKn, and a symbol (BUS) denotes a read request and data transferred on a bus BUS. Data read from the magnetic disk drives DSK
1
-DSKn in response to a read request from a user are transferred on the bus BUS. The magnetic disk drives DSK
1
-DSKn are connected together via the bus BUS, and perform data read process with respect to a read request applied via the bus BUS. Then, the magnetic disk drives DSK
1
-DSKn buffer read data and transfer the read data via the bus BUS. Hence, the read request and read data alternately appear on the bus BUS. Each of the magnetic disk drives DSK
1
-DSKn performs the read process in response to the read request, and sends the read data to the bus BUS.
The magnetic disk drives are sequentially accessed so that unit data D
1
, D
2
, . . . are sequentially read from the magnetic disk drives DSK
1
, DSK
2
, . . . Free or idle times are provided in access time slots which are not identical times with respect to the magnetic disk drives DSK
1
-DSKn, so that an access modification can be handled. In
FIG. 2
, blocks of broken lines denote idle access time slots.
FIG. 3
is a sequence diagram of a write operation, which was proposed in the prior Japanese Patent Application which is not laid-opened or published and is thus not prior art. As shown in
FIG. 2
, the symbols (DSK
1
)-(DSKn) indicate access states of the magnetic disk drives DSK
1
-DSKn, and the symbol (BUS) denotes a read request and data transferred on the bus BUS.
FIG. 3
shows a case where a read request and a write request coexist. The read process is carried out for the read request as has been described above, and data is transferred via the bus BUS. The write process is performed so that write data following the write request is input to a corresponding one of the magnetic disk drives DSK
1
-DSKn. That is, the data is written into the magnetic disk drives DSK
1
-DSKn for each unit data, namely, WD
1
, WD
2
, . . .
For example, in the write process in the magnetic disk drive DSK
3
, the write request and write data are input thereto before the immediately previous read process is completed. Hence, the read process immediately before the write process is completed, and it is necessary to make the time slot idle, as indicated by the broken line. Hence, as shown in
FIG. 3
, by providing the idle time slot, the access time slot immediately thereafter can be used for writing.
FIGS. 4A and 4B
show two states of a schedule table, which was proposed in the prior Japanese Patent Application which is not laid-opened or published and is thus not prior art. The scheduling is carried out so that n·m+k is satisfied where n is the sum of the maximum number of users and the number of idle access time slots, m is an integer equal to or greater than 1, and k is an integer that satisfies a condition 1≦k<n. For example, n=7, m=5 and k=1, the maximum number of users is 34, and the number of idle access time slots is 2.
The schedule table as shown in
FIGS. 4A and 4B
needs an area equal to at least twice the above-mentioned condition (n·m+k). A pointer is used to indicate a position to be referenced, and specified information concerning the magnetic disk drive located at the pointed position and user information are read. Then, a command to the specified magnetic disk drive (storage part) is issued. The same content as described above is written into an area located with an access cycle T starting from the position indicated by the pointer. That is, the same user information is written into two areas spaced apart therefrom at an interval equal to the cycle T of the schedule table. The pointer is sequentially moved at given time intervals, and the access control of the storage device can be carried out in accordance with the user information in the area indicated by the pointer and the corresponding magnetic disk drive.
For example, as shown in
FIG. 4A
, specified information concerning the magnetic disk drive DSK
1
and user A information are stored in the area indicated by the pointer. Specified information concerning the magnetic disk drive DSK
2
to be next accessed and user A information are stored in the area located after the access cycle T from the above area in which the specified information concerning the drive DSK
1
and the user A information are stored. When an access command to the magnetic disk drive DSK
1
in the area indicated by the pointer is issued to the storage device by a control device, the user A information corresponding to the magnetic disk drive DSK
1
located in the pointed position is deleted.
Next, as shown
Aoki Takahiro
Mizutani Masami
Tanaka Ryuta
Bataille Pierre-Michel
Fujitsu Limited
Helfgott & Karas P.C.
Kim Matthew
LandOfFree
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