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1. (WO1998050858) METHOD OF INCREASING THE STORAGE CAPACITY OF A LEVEL FIVE RAID DISK ARRAY, AND EXPANDED ARRAY PRODUCED BY SUCH METHOD

Pub. No.:    WO/1998/050858    International Application No.:    PCT/US1998/009487
Publication Date: Fri Nov 13 00:59:59 CET 1998 International Filing Date: Sat May 09 01:59:59 CEST 1998
IPC: G06F 3/06
G06F 11/10
Applicants: UNISYS CORPORATION
Inventors: LEGG, Christopher, B.
Title: METHOD OF INCREASING THE STORAGE CAPACITY OF A LEVEL FIVE RAID DISK ARRAY, AND EXPANDED ARRAY PRODUCED BY SUCH METHOD
Abstract:
The storage capacity of a Level Five RAID array on an initial set of disks (Disks 0, 1 and 2 in Fig. 4) is expanded by the steps of: A) adding to the rows of the array, new data blocks (D10 thru D19 in Fig. 4) but no parity blocks which reside on an additional set of disks (Disks 3 and 4 in Fig. 4); and, B) initializing the new data blocks such that the exclusive-or of their content in each row of the array is zero (Fig. 5). Due to these steps A) and B), the need to rewrite the original data blocks and parity blocks on the initial set of disks as part of the expansion process is eliminated, and thus the expansion of the array occurs quickly. Alternatively, the storage capacity of a Level Five RAID array on an initial set of disks (Disks 0, 1 and 2 in Fig. 4) is expanded by the steps of: A) changing a parity block (e.g. - P(6, 7, 16, 17 in Fig. 4) to a data block (D16 in Fig. 5) in a particular row on the initial set of disks, without altering the content of the changed block; B) adding in that particular row, one new parity block (P(16, 6, 7, 17 in Fig. 7) and N-1 new data blocks (D17 in Fig. 7) which reside on an additional set of N disks (Disks 3 and 4 in Fig. 7); and, C) initializing that new parity block and new data blocks such that the exclusive-or of their content is zero (Fig. 8). By these steps A)-C), the need to rewrite the original data blocks and parity blocks on the initial set of disks is again eliminated; and further the additional set of disks contains a parity block as well as data blocks.