Patent ID: 7831750

Claim:
A method for processing input/output (I/O) requests for a mirrored storage volume in recovery mode, said method comprising the steps of: a) accessing a recovery map arranged to indicate each region of a mirrored volume for which one or more prior I/O requests were in progress but incomplete prior to said mirrored volume being placed in recovery mode; b) receiving a further I/O request for one or more regions of said mirrored volume in recovery mode; c) determining whether one or more of said regions is within a part of said mirrored volume not yet recovered; d) determining whether one or more of said regions is marked as dirty in said recovery map for said mirrored volume; e) if one or more of said regions is within a part of said mirrored volume not yet recovered and none of said regions is marked as dirty in said recovery map then processing said further I/O request as a normal I/O request; f) based on one or more of said regions being within a part of said mirrored volume not yet recovered and not marked as dirty in said recovery map, recording the one or more regions in an active map for said volume and writing said active map to storage prior to initiating said write request; and g) when one or more of said regions corresponding to said write request is marked as dirty in said recovery map then the step of writing said active map to disk is omitted; wherein said recovery mode recovers the mirrored storage volume from a failure and during said recovery mode, said mirrored volume is synchronized.