Electrical computers and digital processing systems: memory – Storage accessing and control – Hierarchical memories
Reexamination Certificate
2000-03-17
2004-06-08
McLean-Mayo, Kimberly (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Hierarchical memories
C711S134000, C711S136000, C711S159000, C711S160000
Reexamination Certificate
active
06748494
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority of Japanese Patent Application No. 11-088073, filed Mar. 30, 1999, the contents being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a file control device to control an external storage device in a data processing system. More particularly, the present invention relates to a file control device suitable for controlling multiple disk storage devices.
2. Description of the Related Art
The use of magnetic disk devices and other types of storage devices to store data for computer systems is well-known. Storage devices inherently have physical storage contents, which physical storage contents may be used as a logical storage device or as multiple logical storage devices. In particular, in some computer systems, a single physical storage device may be used as a single logical storage device. In other computer systems, a single physical storage device may be used as multiple logical storage devices. Conversely, multiple physical storage devices may also be used as a single logical storage device.
For example, a file control device for a computer system may perform emulation to provide a configuration which makes it look like there are multiple small capacity logical storage devices in a large capacity physical storage device. Furthermore, a file control device may perform emulation to provide a configuration which makes it look like there is one large capacity logical storage device made up of multiple small capacity storage devices. The above-described emulation is performed when the number of physical storage devices is increased to prevent changes in the software which accesses the physical storage devices.
When a single physical storage device is used as a single logical storage device, the capacity of the logical storage device also exists in the capacity of the physical storage device. Therefore, every time that the capacity of a physical storage device is changed, the software which controls access must be revised. If the software were not revised, the software would not be capable of accessing a storage device with a new logical capacity. New types of physical storage devices are being developed every day, and because of the great many varieties of physical storage devices which exist, revising the software to correspond to the physical storage device has become a serious problem.
File control devices logically emulate devices with a specific storage capacity. If control of the logical storage device and control of the physical storage device are separated, then no problems will occur even when a physical storage device with a new capacity is connected to the file control device. Software which controls access to storage devices can handle new storage devices in the same way as the prior art devices. This is advantageous in that the software does not need to be revised.
Therefore, as the capacity of the physical storage device increases, the method whereby multiple logical storage devices are emulated in a single physical storage device has come into widespread use. In emulating the multiple logical storage devices, the software focuses on accessing the logical storage devices. As a result, the software sometimes simultaneously accesses different logical storage devices which are allocated to a single physical storage device. When this happens, a single logical storage device is read and written simultaneously and it must wait for access to other logical storage devices.
In a computer system which uses a large-scale computer, only a single access to a single storage device can be issued at one time. As a result, when a physical storage device and a logical storage device coincide, waiting for access to other logical storage devices does not occur. Therefore, when multiple logical storage devices are configured in a single physical storage device (that is, when a physical storage device and a logical storage device are separated), it looks as if the performance relative to access from the server has declined.
In order to alleviate the decline in access performance, file control devices are typically provided with a disk cache which makes it possible to make multiple accesses simultaneously. A portion of the contents of the logical storage device are stored in the disk cache.
If it is assumed, for example, that two logical storage devices are allocated to a physical storage device, and if the various data which are retained in the two logical storage devices are stored in the disk cache, then either of the data can be accessed simultaneously. However, if data which are retained in one logical storage device are stored in disk cache, and data which are retained in the other logical storage device are not stored in disk cache, then one set of data is transferred from disk cache and the other set of data, which is not stored in disk cache, is transferred from the physical disk.
As described above, by using disk cache, the server increases the possibility of simultaneously accessing data which are retained in multiple logical devices allocated to a single physical storage device. Therefore, when data read processing and data write processing are generated simultaneously between a certain physical storage device and cache memory, the possibility of simultaneously accessing data which are retained in multiple logical devices increases strikingly. The possibility of access to a single logical storage device also comes to mind.
However, the prior art disk cache control does not take into consideration multiple logical storage devices existing in a single physical storage device. More specifically, according to the prior art disk cache control, only the access frequency relative to the logical storage device is used in monitoring the data in disk cache. However, the access frequency relative to the physical storage device has not been used to monitor the data in disk cache. Therefore, there are times when the original effect cannot be obtained sufficiently in the disk cache by providing cache memory.
This problem will now be described in greater detail with reference to
FIG. 9
, which is a block diagram of a prior art file access device. As shown in
FIG. 9
, the prior art file access device includes a storage device
20
having a file control device
30
, two Server InterFace Modules (SIFM)
33
-
1
and
33
-
2
, k Device InterFace Modules (DIFM)
34
-
1
to
34
-k, k physical storage devices
21
-
1
to
21
-k, and two buses
35
-
1
and
35
-
2
for access to a cache memory
40
. Furthermore, the respective single physical storage devices
21
-
1
to
21
-k are configured of two logical storage devices (
50
-
1
,
51
-
1
to
50
-k,
51
-k).
A controller
31
, which is provided in the file control device
30
of the storage device
20
, comprises a control memory
41
. A cache memory monitoring table
42
is stored in the control memory
41
. The cache memory monitoring table
42
includes information indicating a relationship between a position (block) inside the storage device
20
in which data is stored and a position inside the cache memory
40
where a copy of that data is stored.
FIG. 10
is a diagram of a prior art cache memory monitoring table
42
used to monitor the data stored in cache memory
40
. The cache memory monitoring table
42
is used to monitor block units. As described herein, a “block” is a copy of part of the data retained in the storage device
20
. The cache memory monitoring table
42
has, for example, a structure in which a block entry
60
is arranged in order of priority.
One well-known method of data substitution in cache memory
40
is the “least recently used” (LRU) method. In accordance with the LRU method, a control system gives the highest priority to the data that has been most recently accessed, and gives the lowest priority to the data for which the most time has elapsed since it was last accessed.
As shown in
FIGS. 9 and 10
, the data in a block E of logical storage device
11
Fujitsu Limited
McLean-Mayo Kimberly
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