Electrical computers and digital data processing systems: input/ – Input/output data processing
Reexamination Certificate
1998-12-21
2001-12-11
Shalwala, Bipin (Department: 2673)
Electrical computers and digital data processing systems: input/
Input/output data processing
C714S002000
Reexamination Certificate
active
06330620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arrayed I/O unit close decision method and apparatus and a medium containing an arrayed I/O unit close decision program and in particular, to an arrayed I/O unit close decision method and apparatus for controlling a timing to close out from a system an arrayed I/O unit which has frequently caused an operation failure, as well as a medium containing an arrayed I/O unit close decision program.
2. Description of the Related Art
Suppose as an arrayed I/O apparatus, a disc array system in which a plurality of disc units are arranged in an array. Each of the arrayed disc units has normally a retry circuit. When one of the arrayed I/O units is accessed and a data read-out or write-in fails, the retry circuit tries to repeat the read-out or write-in operation. If this retrial is successful, i.e., the read-out or the write-in operation is completed successfully by this retrial, the currently executed processing is continued as it is.
On the other hand, if the retrial is unsuccessful and a predetermined number of retrials is reached, it is decided that the operation failure cannot be eliminated by retrial and the arrayed disc unit accessed is closed out from the system.
Here, the retry circuit executing the retrial should execute various processes required for the retrial operation such as an initial error detection, an error latch release, a fall back operation for re-executing a transaction, a mechanical positioning, and the like. For this, the processing time required for retrial is usually 100 times more than a processing time required for a normal access operation.
However, in the aforementioned conventional example, even if the number of retrials is limited to once, the disc unit which has caused an access error will not be closed from the system if the access error is eliminated by one retrial. Accordingly, if that disc unit is frequently accessed, the retrial is repeated each time, increasing the average transaction processing time, disabling the practical use of the system.
Suppose one retrial requires a time equal to N times of a time Tn required for a normal operation. If an operation failure occurs with a probability P, an average transaction processing time Tv is calculated as follows.
Tv
=
(
1
-
P
)
×
Tn
+
P
×
N
×
Tn
=
Tn
+
(
N
-
1
)
×
P
×
Tn
(
1
)
Here, the second term in Expression (1) represents a transaction processing delay time caused by an operation failure. If the value of N becomes 100 times, the average transaction processing time is doubled even if the P is 1%. Suppose P is 50% which is a conventional limit value for close, then the average transaction processing time becomes 50 times more than a normal operation. That is, the aforementioned system cannot be used in practice.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an arrayed I/O unit close decision method and apparatus capable of closing an I/O unit having an increased “ratio” of access failure so as to maintain a system performance decrease within an allowable range, enabling to assure a system reliability, as well as to provide a medium containing a close decision program.
The arrayed I/O unit close decision method according to the present invention (as claimed in claim
1
) comprises: an initialization step for setting an initial value A in a counter; an upgrade step for adding a constant B to the counter upon a normal operation of an I/O unit in response to an access; a downgrade step for subtracting a constant C from the counter upon an operation failure on an I/O unit in response to an access which failure can be eliminated by a retrial; and a close step for closing an I/O unit whose counter value has become below a value E.
Here, an I/O unit includes a disc apparatus, a disc control apparatus, a semiconductor memory, and other various apparatuses for a data input/output as well as an output apparatus having no input function. Moreover, if B×C>0, these parameters may be negative or positive. It should be noted that “below the value E” may mean literally “smaller than the value E” if (E−A)<0, or “greater than the value E” if (E−A)>0. (This also applies to claims
3
and
5
).
The arrayed I/O unit close decision method according to the present invention (as claimed in claim
2
) may further comprise a limit step for resetting a counter to a threshold value if the counter exceeds the threshold value D.
Here, B×(A−D)≦0 should be satisfied. It should be noted that “exceeds D” may mean literally “greater than D” if (A−D)≦0 or “smaller than D” if (A −D)≧0. (This also applies to claims
4
and
6
.).
The arrayed I/O unit close decision apparatus according to the present invention (as claimed in claim
3
) comprises: an initialization block for setting an initial value A in a counter; an upgrade block for adding a constant B to the counter upon a normal operation of an I/O unit in response to an access; a downgrade block for subtracting a constant C from the counter upon an operation failure of an I/O unit in response to an access which failure can be released by a retrial; and a close block for closing an I/O unit whose counter value has become below a value E.
The arrayed I/O unit close decision apparatus according to the present invention (as claimed in claim
4
) may further comprise a limit block for resetting a counter value to a threshold value D when the counter value has exceeded the threshold value D.
The medium according to the present invention (as claimed in claim
5
) contains an arrayed I/O unit close timing decision program to be executed by a computer, the program causing to: set an initial value A in a counter; add a constant B to the counter upon a normal operation of an I/O unit in response to an access; subtract a constant C from the counter upon an operation failure of an I/O unit in response to an access which failure can be eliminated by a retrial; and close an I/O unit whose counter value has become below a value E.
The arrayed I/O unit close timing decision program (as claimed in claim
6
) may further cause to reset a counter value to a threshold value D when the counter value has exceeded the threshold value D.
In the aforementioned configurations claimed in claims
1
,
3
, or
5
, if an I/O unit causes a number of retrials for its operation failure, the I/O unit is immediately closed. Even when the number of retrials is small for one operation failure, if the I/O unit which has caused the failure is accessed frequently, i.e., the operation failure occurs frequently, the I/O unit is promptly closed
In the aforementioned configurations claimed in claims
2
,
4
, or
6
, an I/O unit which has been operating normally is also immediately closed if it suddenly fails to operate normally, increasing the failure occurrence frequency.
Here, explanation will be given on the aforementioned parameters A, B, C, and D.
In an information processing system, firstly, it is necessary to estimate a transaction processing time Vn required during a normal operation, and a transaction processing time Vr required when an operation failure occurs. The Vn depends on the information processing system but practically can be handled as a constant, assuming a load state of information processing during a normal operation. Moreover, the Vr can also be handled as a constant, assuming the maximum retrial time which may be caused in the information processing system or a case of operation failure having the highest probability in the information processing system.
Next, assuming a case of an operation failure which has occurred with a high probability, it is necessary to set a largest average transaction time Va that can be allowed by the information processing system and a close allowing time Xa. For example, when the average transaction time Va is Ma times more than in a normal operation mode, the close allowing time is set to Xa. In this case, if the operation failu
McGinn & Gibb PLLC
NEC Corporation
Patel Nitin
Shalwala Bipin
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