EP0521630A2
Expired / Lapsed
EP
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DASD array hierarchies
Assignee: International Business Machines Corp
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Filing: 1992-06-16
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Granted: —
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Expires: 2012-06-16
Abstract
Abstract Described is a storage subsystem which takes the form of an array hierarchy comprising a plurality of RAID 3 arrays attached to a common control unit to form a RAID 5 array. Such a hierarchy achieves the concurrency of the RAID 5 array, and the bandwidth and degraded mode operation sustainable by a RAID 3 array. In the event of a DASD failure, the number of devices involved in rebuilding and re-writing missing data to a spare logical device is minimised. Also, disclosed is the accessing of variable length (CKD) records on the array hierarchy, an array hierarchy in which RAID 5 arrays have dissimilar number of logic devices (lower level RAID arrays) and interleave depths; the formation of logical arrays using fractional storage defined onto real DASD subsets; and the defining of logical devices onto DASDs distributed in the same or different physical clusters of DASDs and the rebuild operation thereof. <IMAGE>
Inventors
- 👤 Jaishankar Moothedath Menon
- 👤 Leighton Christopher Wood, Jr.
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 14:35
CPC Classifications
G; G06; G06F; G06F11/00; G06F11/07; G06F11/08; G06F11/10; G06F11/1076; G06F2211/00; G06F2211/10; G06F2211/1002; G06F2211/1045
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
129 words
A storage subsystem comprising: a plurality of RAID 3 arrays of direct access storage devices (DASDs), each RAID 3 array including N data + P parity DASDs attached to a local controller; a common control unit attached for communication to the plurality of RAID 3 arrays to form a RAID 5 array of logical devices, each logical device comprising a RAID 3 array, the RAID 3 arrays being addressable through a path including the control unit and local controllers; and means including the control unit responsive to a data string formed from K*N blocks for segmenting the string into N blocks, encoding P parity blocks over each segment, and writing K of the N+P block segments in column major order of predetermined interleave depth on to counterpart logical devices.
Claim 2
Dependent Claim
42 words
A storage subsystem as claimed in claim 1, wherein said segmenting, encoding, and writing means further includes means for recording the N+P blocks of each logical device onto N+P DASDs of a counterpart RAID 3 array through a path including its controller.
Claim 3
Dependent Claim
141 words
A storage subsystem as claimed in claim 2, wherein the control unit is attached to a subset of the plurality of devices to form a RAID 5 array of logical devices, others of the plurality being reserved as spare devices; the subsystem further comprising: second means including the control unit for detecting a DASD failure in the RAID 3 DASD array counterpart of a logical device and for writing to the logical devices in the designated order and depth and recording the blocks but for those blocks destined for the failed DASD; and third means for rebuilding and rewriting N+P DASDs of the logical device whose counterpart RAID 3 array contains the failed DASD onto the spare device on either a predetermined or opportunistic schedule, said rebuild and rewrite spanning only the spare device and said device having the failed DASD.
Claim 4
Dependent Claim
110 words
A storage subsystem as claimed in claim 3, wherein the plurality of RAID 3 arrays further comprises a first RAID 5 array of m logic devices and a second RAID 5 array of n logic devices, m not equal to n; the control unit further comprises means for switchably coupling the control unit to any one of the RAID 5 arrays; and the first means including the switching means further comprises means for selecting any of the RAID 5 arrays and recording segments on the logic devices thereof in column major order thereon to an interleave depth distinguishable from the interleave depth of at least one other RAID 5 array.
Claim 5
Dependent Claim
172 words
A storage subsystem comprising: a plurality of logical devices, each device formed from a RAID 3 array of DASDs; a control unit for communicatively attaching either a first or a second RAID 5 array of the logical devices; first means including the control unit for selecting the first RAID 5 array, segmenting a data string into segments of m data blocks, coding p parity blocks over each segment, and writing each segment of m data + p parity blocks across the logical devices of the first array in column major order to a first interleave depth; and second means including the control unit for selecting the second RAID 5 array, segmenting another data string into n data blocks, coding p parity blocks over each segment, and writing each segment of n data + p parity blocks across the second DASD subset in column major order to a second interleave depth, at least one of the devices of the second RAID 5 array being also a member of the first RAID 5 array.
Claim 6
Dependent Claim
46 words
A storage subsystem as claimed in claim 5, wherein at least one logical device DASD of the plurality reserves a fraction of its storage capacity to the first and the second RAID 5 arrays proportional to the number of logical devices in each RAID 5 array.
Claim 7
Dependent Claim
26 words
A storage subsystem as claimed in claim 6, wherein n is not equal to m, and the second depth is not equal to the first depth.
Claim 8
Independent Claim
91 words
A method for writing data to and from a plurality of DASDs, comprising the steps of: configuring the plurality of DASDs into a RAID 5 array of logical devices, each logical device including N data + P parity DASDs configured as a RAID 3 DASD array; and segmenting each data string into K logical records of N data blocks each, coding P parity blocks over each segmented record, and writing the K logical records in column major order of predetermined interleave depth onto the logical devices of the RAID 5 array.
Claim 9
Independent Claim
157 words
A method for managing data transfer to a storage subsystem, said subsystem being formed from a plurality of RAID 3 DASD arrays, each RAID 3 array having N data + P parity DASDs attached to a controller, comprising the steps of: configuring the plurality of RAID 3 DASD arrays into a RAID 5 array of addressable logical devices by communicatively attaching each of their controllers through a common control unit ; and segmenting a string of data at the common control unit into K logical records of N blocks each, parity coding each logical record and adding P blocks thereto, and writing K logical records of N+P blocks, each in column major order of predetermined interleave depth, onto the RAID 5 array of logical devices such that the N+P blocks of each logical record are recorded onto N+P DASDs of a counterpart RAID 3 array operating as the addressed logical device through a path including its controller.
Claim 10
Dependent Claim
120 words
A method as claimed in claim 9, further comprising: reserving at least one of the logical devices as a spare device during the configuring step; accessing the logical devices, other than the spare device, through a path including the common control unit in column major order of predetermined interleaved depth; detecting a DASD failure in a RAID 3 array; responsive to detection of said failure, accessing the logical devices except for the failed DASD; and rebuilding and rewriting N+P DASDs of the logical device whose counterpart RAID 3 array contains the failed DASD onto a spare device on either a predetermined or opportunistic schedule, said rebuild and rewrite spanning only the spare device and said device having the failed DASD.
Claim 11
Dependent Claim
90 words
A method as claimed in claim 10, wherein the accessing step further comprises: accessing K*(N+P) blocks from the array in row major order K modulo M and in column major order K module M*(N+P), M lying in the closed integer interval (1,K); and executing large and small access requests over the RAID 5 array such that a minimum number X of blocks transferred to achieve the maximum data rate for a given M lies in the closed interval ((N+P-1, (N+P-1)*K) whose end points are defined by M=1 and M=K respectively.
Claim 12
Dependent Claim
92 words
A method as claimed in claim 10 or claim 11, wherein the step of accessing all but the failed DASD in the RAID 3 array of an accessed logical device responsive to a small read access further includes: reading all but the failed DASD and reconstructing any unavailable data block by logically combining the N+P-1 available blocks; and writing to all but the failed DASD such that the parity block and all but one of the data blocks are stored on the remaining DASDs of RAID 3 array of the accessed device.
Claim 13
Independent Claim
241 words
A method for writing variable length count-key-data (CKD) field formatted records to a storage subsystem, said subsystem being formed from a plurality of RAID 3 DASD arrays, each RAID 3 array having N data + P parity DASDs attaching a controller, comprising the steps of: configuring the plurality of RAID 3 DASD arrays into a RAID 5 array of addressable logical devices by communicatively attaching each of their controllers through a common control unit ; and segmenting each data string at the common control unit into K logical records of N stripes each, parity coding each logical record and adding P strings thereto, and writing K logical records of N+P strings, each in row major order of predetermined interleave depth, onto the RAID 5 array of logical devices such that the N+P strings of each logical record are recorded onto N+P DASDs of a counterpart RAID 3 array operating as the addressed logical device through a path including its controller such that: each count field of a CKD formatted variable length record being replicated on the N DASDs of the first device in row major order, the key and data fields following the count field of a CKD formatted variable length record are segmented and recorded across N DASDs of the counterpart RAID 3 array operating as the addressed logical device in the predetermined row major order and interleave depth, and each parity block P logically combining a counterpart N fields.
References Cited (Backward Citations)
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