Electrical computers and digital processing systems: memory – Storage accessing and control – Hierarchical memories
Reexamination Certificate
1998-11-20
2002-11-12
Kim, Matthew (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Hierarchical memories
C711S129000, C711S153000, C711S156000, C711S170000, C711S113000
Reexamination Certificate
active
06480936
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a storing apparatus having a cache function for developing write data into a data buffer area in response to a write access of a host, notifying of a normal end, and writing back the write data in the data buffer area into a storing medium. More particularly, the invention relates to a storing apparatus for dynamically changing a buffer construction in accordance with a random access and a sequential access from a host.
2. Description of the Related Arts
Attention is paid to an optical disk as a storing medium serving as a nucleus of multimedia which has rapidly been developing in recent years. For example, as for an MO cartridge of 3.5 inches, MO cartridges of 128 MB, 230 MB, 540 MB, 640 MB, and the like are provided. An optical disk drive using such an MO cartridge is provided as an external storing apparatus of a personal computer. The optical disk drive is, however, known as an apparatus which takes longer time in the writing operation as compared with the reading operation. That is, in the reading operation of the optical disk, a laser beam of an optical head is sought to a target track (on-track), data as a target is read during one rotation of the medium in the on-track state, and the read data can be responded to the host. On the contrary, the writing operation of the optical disk needs operations for erasing, writing, and verification reading corresponding to three rotations of the medium in the on-track state where the laser beam of the optical head is sought to the target track, so that the writing operation takes time. Although there is also a direct overwrite corresponding optical disk in which the erasing and writing operations can be simultaneously performed, a writing time corresponding to two rotations of the medium including the verification reading is necessary. In the storing apparatus in which the writing operation is slower than the reading operation as mentioned above, there is provided a cache control function such that when a write access is received from the host, the write data is developed into a data buffer area in a memory, a normal end is notified to the host, the writing operation is finished when it is seen from the host, and after that, the write data developed in the data buffer area is written into a storing medium. In such a conventional cache control function, for example, when it is predicted that a frequency of the sequential access in which write addresses continue is high as a write access from the host, a buffer construction such that a data buffer area in the memory is set to a single section is set by a setup process of the storing apparatus. With such a buffer construction of the single section, after the continuous write data was developed into the buffer by the sequential access of the host of an amount corresponding to the data buffer area, the write data can be written into the medium in a lump. The number of seeking times when the write data developed in the data buffer area is written back to the medium is reduced and whole access performance can be enhanced. When it is predicted that the frequency of the random access in which the write addresses are discontinuous as a write access from the host is high, a buffer construction such that the data buffer area in the memory is divided into sections as many as possible by the setup process of the storing apparatus is set. With such a buffer construction in which the number of sections is large, an empty section can be efficiently prepared for the random access of the host, so that the write data can be developed into the empty section without waiting for an empty buffer section and the write access when it is seen from the host can be promptly and normally finished.
In recent years, however, there is a case where a plurality of hosts are connected to one storing apparatus and the storing apparatus is used as common resources, and the frequency of the sequential access and that of the random access are different depending on the host. On the contrary, the buffer construction of the storing apparatus is fixedly determined to either the sequential correspondence or the random correspondence. Consequently, when the write access from the host which is not adapted to the buffer construction frequently occurs, there is a problem such that the write data in a write waiting state to the medium remains in the data buffer area, the write access of the host becomes slow due to the waiting for the empty section in the buffer, and the whole access performance deteriorates. In order to reconcile the sequential access and the random access, a method of setting the number of sections in the data buffer area to the intermediate number between the number of sections of the sequential access and that of the random access. In this case, however, the efficiency deteriorates for both of the sequential access and the random access and the whole access performance is not improved.
SUMMARY OF THE INVENTION
According to the invention, there is provided a storing apparatus in which an access efficiency is raised by optimizing a buffer construction for both of a random access and a sequential access from a host.
A storing apparatus of the invention comprises a cache control unit, an access kind discriminating unit, and a buffer construction control unit. When a write access is received from an upper apparatus, the cache control unit develops write data into a data buffer area in a memory, notifies the upper apparatus of a normal end, and after that, writes the write data developed in the data buffer area into a storing medium. The access kind discriminating unit discriminates whether the write access of the upper apparatus is a random access in which write addresses are discontinuous or a sequential access in which the write addresses are continuous. The buffer construction control unit sets either a random corresponding buffer construction which enables a buffer development and a medium writing that are suitable for the random access or a sequential corresponding buffer construction which enables a buffer development and a medium writing that are suitable for the sequential write access. When the sequential access is decided in a setting state of the random corresponding buffer construction, the buffer construction control unit changes the construction to the sequential corresponding buffer construction. When the random access is decided in a setting state of the sequential corresponding buffer construction, the buffer construction control unit changes the construction to the random corresponding buffer construction. In the storing apparatus of the invention, therefore, whether the write access from the host is the sequential access or the random access is analyzed, the data buffer construction having the optimum number of sections is selected in accordance with the access kind, and the caching operation is executed, thereby optimizing the buffer development and the medium writing in response to the write access of the host and improving the efficiency. For example, when the host performs the sequential access, the number of sections in the data buffer area is reduced and the operation is executed, thereby increasing a write data amount per time to the medium and reducing the number of times of the writing to the medium. On the contrary, when the host executes the random access, by increasing the number of sections in the data buffer area, the buffer is efficiently developed. Even in case of the random access, by developing the write data of the continuous addresses every section, the number of times of the writing to the medium is reduced. When the write data amount by the sequential access reaches a predetermined value in the setting state of the random corresponding buffer construction, the buffer construction control unit changes the data buffer area from the random corresponding buffer construction to the sequential corresponding buffer construction. For example, when the write data amount by the sequential write ac
Ban Akira
Ichii Hiroshi
Chace Christian P.
Greer Burns & Crain Ltd.
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