Method and means for accessing DASD arrays with tuned data transfer rate and concurrency
First Claim
1. A method for managing accesses received from an external source to at least one logical track having KN sequentially ordered blocks distributed and stored onto an array of N DASDs in which a single parameter M specifies the trade off between data rate and concurrency, each DASD including a cyclic track recording medium, each track having a storage capacity of K blocks, said array including control means for securing synchronous access to selectable ones of the N DASDs, comprising the steps at the control means of:
- (a) formatting and writing of the KN blocks onto N tracks of the N DASDs of the array responsive to a command from said source specifying a value for parameter M, said blocks being written on said N tracks in row major order K modulo M and in column major order K module MN, M being less than or equal to K; and
(b) executing access requests over the array from said external source such that each access of any subset of KN blocks formatted and written according to step (a) constitutes a synchronous data exchange of b blocks at a time with b counterpart DASDs and further such that (N-b) DASDs are concurrently available for binding to another access request, M being inversely related to b.
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Abstract
A method and means for managing access to a logical track of KN blocks of which K are parity blocks. The KN blocks are distributed and stored in an array of N DASDs having K blocks per physical track per DASD. The array includes control means for securing synchronous access to selectable ones of the DASDs responsive to each access request. The method involves (a) formatting the blocks onto the array using a row major order modulus as the metric for balancing the data rate and concurrency (the number of DASDs bound per access) and (b) executing the random sequences of large and small access requests over the array.
100 Citations
10 Claims
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1. A method for managing accesses received from an external source to at least one logical track having KN sequentially ordered blocks distributed and stored onto an array of N DASDs in which a single parameter M specifies the trade off between data rate and concurrency, each DASD including a cyclic track recording medium, each track having a storage capacity of K blocks, said array including control means for securing synchronous access to selectable ones of the N DASDs, comprising the steps at the control means of:
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(a) formatting and writing of the KN blocks onto N tracks of the N DASDs of the array responsive to a command from said source specifying a value for parameter M, said blocks being written on said N tracks in row major order K modulo M and in column major order K module MN, M being less than or equal to K; and (b) executing access requests over the array from said external source such that each access of any subset of KN blocks formatted and written according to step (a) constitutes a synchronous data exchange of b blocks at a time with b counterpart DASDs and further such that (N-b) DASDs are concurrently available for binding to another access request, M being inversely related to b. - View Dependent Claims (8)
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2. A method for managing access to at least one logical track of KN blocks of which K are partly in which a single parameter M specifies the trade off between data rate and concurrency, said KN blocks being distributed and stored in an array of N DASDs, each DASD including a cyclic track recording medium, each track having a storage capacity of K blocks, said array including control means responsive to read and write accesses from an external source for securing synchronous access to selectable ones of the N DASDs, comprising the steps at the control means of:
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(a) formatting and writing of the KN blocks onto N tracks of counterpart N DASDs of the array responsive to a command from said source including a value for parameter M, said blocks being written on said N tracks in row major order K modulo M and in column major order K modulo MN, M lying in the closed integer interval (1,K); and (b) executing access requests from said external source over the N DASDs of the array such that each access of any subset of KN blocks formatted and written according to step (a) constitutes a synchronous exchange of b blocks at a time with b counterpart DASDs, and, further such that (N-b) other DASDs are concurrently available for binding to another access request and further such that the minimum number of blocks transferred in order to achieve a maximum data rate lies in the closed interval ((N-1, N-1)K) for any given M. - View Dependent Claims (3, 4, 5, 6, 7)
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9. In a system having a CPU, an array of N DASDs, and means intercoupling the CPU and the array for synchronously accessing selectable ones of the DASDs, said means including means responsive to KN sequentially ordered blocks from said CPU for writing said blocks onto N DASDs in which a single parameter M specifies the trade off between data rate and concurrency, each DASD including a cyclic track recording medium, each track having a storage capacity of K blocks, wherein said intercoupling means further comprise:
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(a) means for formatting and writing the KN blocks onto N tracks of the N DASDs of the array responsive to a command from said CPU including a value for parameter M, said blocks being written on said N tracks in row major order K modulo M and in column major order K modulo MN, M being less than or equal to K; and (b) means for executing access requests over the array from said CPU such that each access of any subset of KN blocks formatted and written according to step (a) constitutes a synchronous data exchange of b blocks at a time with b counterpart DASDs and further such that (N-b) DASDs are concurrently available for binding to another access request, M being an inverse function of b. - View Dependent Claims (10)
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Specification