Storage management based on predicted I/O execution times

Details Storage management based on predicted I/O execution times Storage management based on predicted I/O execution times

1998-02-09

2003-04-22

Peikari, B. James (Department: 2186)

Electrical computers and digital processing systems: memory

Address formation

Address mapping

C711S213000, C711S167000, C711S173000, C710S036000, C710S058000

Reexamination Certificate

active

06553476

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a storage apparatus such as a magnetic disk apparatus etc. and in particular to a storage apparatus for recording and reproducing real-time data such as a image data by controlling a temporary memory circuit built into the storage apparatus and an input/output (I/O) control method for such a storage apparatus.
In recent years, the recording density and the data transfer rate in storage apparatus, such as magnetic disk apparatus, have been ever on the increase. These disk apparatuses are used also for recording and reproducing multi-channel image data.
For image data to be continuously recorded or reproduced at a predetermined rate in a disk apparatus, it is necessary to process an I/O request within a predetermined time in the disk apparatus. Processing a plurality of I/O requests requires accurate time management of each I/O request.
The time management of the I/O requests can be executed by software processing of a host computer for controlling the disk apparatus. Managing I/O requests in real time, however, produces the problem of a heavy load imposed on the CPU. In view of this, as disclosed in unexamined Japanese publication Hei 8-171526, a dedicated interface unit is connected between the disk apparatus and the host computer for time management of I/O requests.
Further, in recording or reproducing multi-channel image data, a temporary memory unit is required to buffer data that would otherwise be lost due to the suspension of data transfer mechanical operations such as the disk apparatus seek operation.
Conventional disk apparatuses, as disclosed in U.S. patent Ser. No. 5,465,343, for example, comprise a temporary memory circuit for improving the storage performance, in which a temporary memory circuit is used as a buffer memory or a cache memory. The temporary memory circuit is used also for prefetching. The prefetching is a process for reading a succeeding data after reading data corresponding to an output request, and storing the succeeding data in the temporary memory unit with the aim of improving the performance of processing sequential data I/O requests.
The conventional storage apparatus using the above-mentioned interface unit and disk apparatus will now be explained with reference to the accompanying drawings.
FIG. 39
is a block diagram showing a general system configuration of the storage apparatus using the above-mentioned interface unit and the conventional disk apparatus. As shown in
FIG. 39
, a host computer
71
, a reference clock generating section
72
and an interface unit
73
are connected to an I/O bus
75
. A disk apparatus
74
is connected to the interface unit
73
through a data bus
76
.
The interface unit
73
includes a bus interface control section
82
(hereinafter called “the bus I/F control section
82
”), an I/O control section
84
, a schedule management section
81
and a queue-with-priority management section
83
. In the interface unit
73
, the schedule management section
81
controls the sequence of execution of I/O requests.
The host computer
71
issues a data I/O request to the interface unit
73
. The I/O request is received through the I/O bus
75
by the I/F control section
82
of the interface unit
73
, and stored in the queue-with-priority management section
83
through a command bus
73
. The queue-with-priority management section
83
manages a queue with priority, a pending queue and an I/O execution queue.
The reference clock information generated in the reference clock generating section
72
passes on the I/O bus
75
, and is stored in the schedule management section
81
through the bus I/F control section
82
.
The schedule management section
81
transfers an I/O request to the queue with priority in the queue-with-priority management section
83
. Upon receipt of the request, the schedule management section
81
determines whether the queue with priority contains an I/O request.
In the case where the queue with priority contains an I/O request, the schedule management section
81
fetches the particular I/O request and determines whether the request has a high order of priority with a specified processing time. In the case where the request has a high priority, the schedule management section
81
transfers the particular I/O request to the I/O control section
84
, while in the case where the priority of the request is low, the schedule management section
81
adds the request to the pending queue.
In the case where no I/O request is contained in the queue with priority, in contrast, the pending queue is checked. In the presence of any I/O request contained in the pending queue, the particular I/O request is fetched and, when it is before the lapse of a set processing time, the fetched I/O request is executed. In the case where the I/O request has passed the set processing time and has timed out, on the other hand, the request is discarded or returned to the pending queue.
The I/O control section
84
controls the disk apparatus
74
, accesses an instruction on data I/O, and executes the data write or read operation.
FIG. 40
is a diagram showing a method for dividing and controlling the buffer memory making up the temporary memory unit of the disk apparatus
314
.
A portion (a) in
FIG. 40
shows an adaptive segmentation method. As shown in the portion (a) of
FIG. 40
, the buffer memory is divided into a plurality of segments which can be assigned to a write buffer and a cache for read data. Also, each segment size can be changed in accordance with the data size to be transferred in response to a write/read command.
A portion (b) in
FIG. 40
shows a fixed segmentation method. In response to a set command from an external system, the buffer memory can be divided into a plurality of segments of fixed size. With the disk apparatus conforming to the SCSI-3 (SCSI: Small Computer System Interface) specification, for example, the number of segments and the size of each segment of the buffer memory can be set appropriately. Each segment size is identical and fixed.
In the above-mentioned conventional control method, the disk apparatus
74
uses the buffer memory divided into segments. As a result, the conventional storage apparatus meets the multi-task requirement in the recording and reproduction of multi-channel image data, and improves storage performance.
Explanation will be made below about certain problems encountered in the conventional storage apparatus configured as described above.
A first problem of the conventional storage apparatus lies in the management of the execution time of an I/O request.
The time for executing an I/O request in the disk apparatus of the conventional storage apparatus is sometimes considerably variable depending on the variations in the time for access to a target area, i.e., the seek time or the waiting time for rotation and the operating conditions of the temporary memory circuit. In the conventional storage apparatus having the above-mentioned configuration, the interface unit and the external system lack means for obtaining information on the time for accessing the disk apparatus and the operating conditions of the temporary memory circuit, and therefore the execution time cannot be accurately predicted. As a result, a time management assuming an excessively long execution time is required for meeting a time limit to ensure that data is not lost, thereby leading to the problem of a deteriorated processing efficiency.
A second problem of the conventional storage apparatus is that the response to an I/O request is occasionally delayed because of deteriorated performance.
In the conventional storage apparatus, an I/O request with high-priority having a time limit is executed preferentially, while an I/O request low in priority is set in pending. In this way, the image data having high-priority are continuously recorded and reproduced. In the case where a high-priority I/O request is not contained in the queue but only low-priority I/O requests are pending, the I/O requests of low priority are executed unconditiona

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