EP0469924A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Method for balancing the frequency of DASD array accesses when operating in degraded mode
Assignee: International Business Machines Corp
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Filing: 1991-08-02
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Granted: —
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Expires: 2011-08-02
Abstract
Abstract A statistically balanced block design or other uniform distribution of parity groups across a DASD array is described for minimizing the additional access loading when operating in failure mode. The new use comprises the steps of (a) forming and writing parity groups according to a balanced block design or equivalent; and (b) accessing remaining DASD's in the array in a minimal referencing pattern as a function of the parity group distribution given the unavailability of a path to data (failed control unit or DASD). <IMAGE>
Inventors
- 👤 Richard Lewis Mattson
- 👤 Spencer Ng
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 09:05
CPC Classifications
G; G06; G06F; G06F11/00; G06F11/07; G06F11/08; G06F11/10; G06F11/1076; G06F11/1008; G11; G11B; G11B20/00; G11B20/10; G11B20/18; G11B20/1833
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
98 words
A method of balancing the frequency of read and write accesses to the direct access storage devices (DASD) of an array comprising C strings of S DASDs, the method comprising the steps of: writing parity groups of data across the DASDs of the array according to a balanced block design, each of said parity groups comprising K-1 data areas plus a parity area, such that when the data on a DASD in one of said strings becomes unavailable, the loading of subsequent read and write operations to said array is uniform across the DASDs in the unaffected strings.
Claim 2
Dependent Claim
137 words
A method as claimed in claim 1 wherein the step of writing parity groups comprises: writing a plurality N of said parity groups such that each DASD is partitioned into N equal sized regions or recording areas and assigning regions to the parity groups such that (1) any two regions in the same parity group are located on different DASD's, (2) each DASD has one region assigned to each one of N different parity groups, and (3) for every pair of DASD's, there are exactly M parity groups containing regions from both DASD's; the method further comprising the step of: responsive to the unavailability of a path to addressible information on a failed DASD, accessing the remaining (C*S)-1 other DASD in a minimal referencing pattern as a function of the uniformity of the distribution of parity groups.
Claim 3
Dependent Claim
47 words
A method as claimed in claim 2, wherein the assignment of regions to the parity groups results in a near uniform distribution of parity groups among the array DASD's, said distribution being selected from the set consisting of balanced incomplete block design, Latin Squares, and Hadamard matrices.
Claim 4
Independent Claim
150 words
A method for balancing the frequency of read R and write W accesses to a C*S array formed from C string controllers and S DASD/string, a parity measure (XOR) being defined over information located on counterpart physical recording areas of K < C*S DASD's, a "parity group" of K recording areas comprising K- 1 data areas + the parity measure, information in any given parity group located on an unavailable DASD being reconstrufted by logically combining (XORing) information retrieved from the K other DASD's, comprising the steps of: (a) forming and writing parity groups of K areas/group approximately uniformly over counterpart DASD's in the array as generated by a deterministic process; and (b) responsive to the unavailability of a path to addressible information on a failed DASD, accessing the remaining (C*S)-1 other DASD in a minimal referencing pattern as a function of the uniformity of the distribution of parity groups.
Claim 5
Dependent Claim
20 words
A method as claimed in claim 4, wherein the deterministic process is selected from a combinatorially generative unbalanced block procedure.
Claim 6
Dependent Claim
30 words
A method as claimed in claim 4 or claim 5, wherein the size K of each parity group is less than the number of controllers C i.e. K < C.
Claim 7
Independent Claim
31 words
A method as claimed in any of claims 4 to 6, wherein the deterministic process is selected from the set consisting of balanced incomplete block design, Latin Squares, and Hadamard matrices.
Claim 8
Independent Claim
72 words
A method as claimed in any of claims 4 to 7, wherein step (a) further comprises the step of allocating the parity groups on the DASD's such that: (1) a given parity group only appears once in any string, and (2) parity groups be placed on the DASDs such that accesses to a failed DASD on one string result in uniformly distributed accesses to the (S*(C-1)) other DASDs on (C-1) other strings.
Claim 9
Dependent Claim
33 words
A method as claimed in claim 8, wherein responsive to a controller failure, reconstructing the data on the unavailable DASD from the other K-1 members of the parity groups on K other strings.
Claim 10
Independent Claim
25 words
A method as claimed in any preceding claim, wherein the number of data areas in at least two of the parity groups are not equal.
Claim 11
Independent Claim
50 words
A method as claimed in any preceding claim, wherein at least one of the DASD in the array includes recording space not dedicated to a parity group, said recording space being of size sufficient to accomodate all or part of a parity group or groups recorded in a sparing mode.
References Cited (Backward Citations)
No citation records indexed.
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