JPS6041125A - Control device of storage device - Google Patents

Abstract

PURPOSE:To prevent data from being lost due to a data buffer error at the rewriting time by connecting an intermediate buffer having capacity corresponding to a fixed length record between a buffer and a fixed length record file device. CONSTITUTION:One fixed length record out of data divided into plural fixed length records stored in a track buffer 16 is transferred to the intermediate buffer 18 and then written in a magnetic disc 12. In case of partial updating of a file, only the corresponding fixed length record is rewritten, and when two files are to be updated, the corresponding fixed length records are written through the buffer 18 twice. If an error is detected at the writing from the buffer 18 to the magnetic disc 12, data left in the buffer 16 are transferred to the buffer 18 and the transferred data are rewritten from the buffer 18 to the disc 12. If an error is detected during transfer from the buffer 16 to the buffer 18, the data are transferred from the disc 12 to the buffer 16 and the writing command is retried.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a control device that performs buffer emulation control for a fixed-length file device such as a magnetic disk.

Prior Art and Problems Magnetic disk drives are used as external storage devices for central processing units (CPUs), and constitute fixed-length record file devices. That is, the disk is divided into a number of concentric circles (referred to as tracks or cylinders), each trunk is provided with a reference point, and each trunk is divided into a plurality of subsections (referred to as tracks or cylinders) of a predetermined length from the reference point.
(called sectors), and access is performed in units of sectors.

Since CPU input/output data has a variable length, when writing CPU output data to a disk, it is necessary to divide the output data into sectors (fixed length records).

In this way, to make one file format appear to be a different file format, or to make a fixed-length record file device isometrically variable-length record file device in the example above, A buffer is provided to temporarily store data, and data is read and written on the buffer. This is called buffer emulation.

Conventionally, when data updated on a buffer is written back to a fixed-length record file device, the buffer data is sent as is to the file device. However, in this method, if an error occurs in the buffer during write-back, data in the file device will also be lost since writing has already started. That is, the buffer used has a capacity that can accommodate data for one track on the disk, and when updating records on the track, access the disk, read all data on the trunk, and fill the buffer. The relevant part of the buffer is rewritten with update data sent from the CPU, and the data in the buffer is then written back to the track. However, since the disk is a fixed-length record file, this To write back, it is necessary to separate one track's worth of data on the buffer into sectors (fixed-length records), and fixed-length records consist of the data read from the disk and the updated data (as a result of partitioning, ), if an error is found in the record as a result of the read-after-write check, the data of the record, that is, part of the data read from the disk and the C
Part of the data sent from the PU is lost (becomes unreliable).

Purpose of the Invention The present invention attempts to prevent data from being lost due to a data buffer error during write-back by providing an intermediate buffer with a capacity equivalent to a fixed-length record between a buffer and a fixed-length record file device. It is something to do.

Structure of the Invention The present invention provides a control device for controlling a fixed-length record storage device as a variable-length record storage device, which includes a buffer for temporarily storing unit data consisting of a plurality of fixed-length records read from a fixed-length record storage device. An intermediate buffer is provided to which a fixed length record is transferred from the buffer, and upon writing, the fixed length record is transferred from the buffer to the intermediate buffer, and the fixed length record is written from the intermediate buffer to a fixed length record storage device. Next, this will be explained with reference to examples.

Embodiment of the Invention FIG. 1 shows an embodiment of the invention, in which reference numeral 10 denotes a host CPU (
12 is an external storage device for fixed-length records, specifically a magnetic disk storage device; 14 is a disk control device equipped with a track buffer 16 and controlled by buffer emulation. The control device 14 includes a host interface circuit 20, a device interface circuit 22, a data transfer circuit 24, and the like, and further includes an intermediate buffer 18 in the present invention. As mentioned above, the track buffer 16 has a storage capacity that can store data for one trunk of the magnetic disk 12, and the intermediate buffer 18 has a storage capacity for one sector (one fixed length record). Although only one magnetic disk 12 is shown in the drawing, in reality, a plurality of magnetic disks 12 are usually provided.

FIG. 2 shows the relationship between fixed-length records, variable-length records, and trunk buffers. fa) indicates the variable length record format, (bl indicates the contents of the track buffer, and (C) indicates the fixed length record format. HA is the home address area, R
o is a record zero area, and R1-Rn are partial record areas. The mark indicates the trunk reference point.

When the host CPU 10 instructs the control device 14 to read by specifying a track number and a record position within the track, the control device reads the magnetic disk 12 using the trunk number.
is accessed, the relevant trunk is read, and the data for one track is taken into the buffer 16. Then, the corresponding record is taken out from the buffer 16 and sent to the host CPU 1'0. When the host cpuio instructs the control unit 14 to write, the control unit receives data from the host CPU, writes it to the buffer 16, and when the writing is completed, divides it into fixed-length records and stores them on the magnetic disk. Write to some trunk. To explain using Figure 2, the same figure (a
If l is variable length data from the host CPU, the trunk buffer 16 takes in the variable length data in a continuous state as shown in +bl in the same figure (the variable length data is taken in sequentially from the beginning), and this is shown in the figure ( As shown in C), each record is subdivided into fixed-length records and sequentially written to the corresponding trunk. Due to this division into fixed length records, the variable length records 1'Ro, R+ to Rn from the boss CPU span two sectors as shown in the figure.

When performing a partial update of a file, a part of the record group stored on the magnetic disk will be modified, but in this case, only the record to be updated is sent from the host CPU, and the data of the corresponding trunk is read and The corresponding record will be replaced with the new record sent from the host cPU. Now, a new record Ri is sent from the host, the corresponding trunk is read, the part corresponding to record Ri is replaced with the above new record, and the record Ri is divided into fixed length records. It is assumed that the first half or the second half of the long record is data read from a magnetic disk. If a record is written and an error occurs as a result of the read-after-write check, the entire record becomes unreliable, and everything including reading one track of data from the disk and sending a new record from the host CPU must be restarted from the beginning. It becomes necessary. Therefore, in the present invention, an intermediate buffer 18 is provided, and writing (updating) is performed as follows.

The data in the track buffer 16 that has been subdivided into fixed-length records is transferred to the intermediate buffer 18 for one fixed-length record, and then written to the magnetic disk 4. In the case of a partial update of a file, only the corresponding fixed-length record (the fixed-length record in which the rewritten record exists) is rewritten, and as mentioned above, if it spans two records, writing via the intermediate buffer 18 is performed twice. Let's go around. If writing occurs multiple times, use 3 intermediate buffers with the capacity of 1 fixed-length record.
Writing can be made continuous by providing two sets and using them alternately (when one is writing, the other is reading, and this is repeated alternately). Sofa 18 to the middle
If an error is found in writing to the magnetic disk 12, the data remains in the trunk buffer 16, so the data can be moved to the intermediate buffer 18 and rewritten from the buffer to the magnetic disk 12. If an error is found in data transfer from the track buffer 16 to the intermediate buffer 18, the data is transferred from the magnetic disk 12 to the track buffer 16, and the write (update) command is retried.

FIG. 3 is a flowchart showing the processing of commands from the host CPU. As shown in the figure, upon receiving a command from the host CPU 10, the control device 1'4 checks whether the command is a write (write), and if it is a write (Y), checks whether data is stored in the track buffer 1G. If the track data is not stored, the relevant track data is read from the external storage device 12 and stored in the hesophagus 16, and with the track data in the buffer, the boss CP is
Receives write record data from U and divides it into fixed length records. Next, a block (fixed length record) to be written is searched for and transferred to the intermediate buffer 18, where parity is checked. If an error is found, try again,
If there is no error, the magnetic disk 1 is transferred from the intermediate buffer 18.
Write to 2. In this way, read-after-write errors are checked, and if an error is found, the above operation of fetching data from the track buffer 16 to the intermediate buffer 18 is repeated, and if no error is found, the process moves on to writing the next fixed-length record. When there are no fixed-length records to write, the write process ends.

If the command is not a write (N), this is a read (
This command checks whether there is a record of the corresponding trunk in the track buffer 16, and if so, sends it from the track buffer to the host CPU.
If not, the corresponding track on the magnetic disk is read, the track data is taken into the buffer 16, and the corresponding record is sent to the host CPU.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, even if an error occurs in the buffer, data is not lost, so data reliability can be improved, and the control device can retry, so O3
There is no need for retries under (operating system), and the load on O8 can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of fixed length and variable length records, and FIG. 3 is a block diagram showing a processing procedure. In the drawing, 14 is a control device, 12 is a fixed-length record file device, 16 is a buffer 1, and 18 is an intermediate buffer. Applicant Fujitsu Ltd. Representative Patent Attorney Minoru Aoyagi Figure 1 Figure 2

Claims (1)

[Scope of Claims] A control device for controlling a fixed-length record storage device as a variable-length record storage device, including a buffer for temporarily storing unit data consisting of a plurality of fixed-length records read from a fixed-length record storage device. , providing an intermediate buffer to which fixed-length records are transferred from the buffer, transferring fixed-length records from the buffer to the intermediate buffer upon writing, and writing the fixed-length records from the intermediate buffer to a fixed-length record storage device; 1. A control device for a storage device, characterized in that the control device