Method and apparatus for establishing and maintaining the status of membership sets used in mirrored read and write input/output without logging

A method of maintaining the status of mirrored disk drives containing redundant copies of data, the method comprising the steps of:

• establishing a cohort set on each of the mirrored disk drive representing a status of the copies stored on the mirrored disk drives, the cohort set containing membership information for redundant copies of data units stored in the plurality of mirrored disk drives, the membership information comprising a data structure of 2n status bits for identifying which disks contain current copies of the data units, where n is the number of disks in the system, wherein the first n bits indicate an intention to update the membership information for the copies and the second n bits indicate a current state of the membership information;
• and
• updating the contents of the cohort sets when a disk drive failure has been detected to reflect unavailability of the copy of data on the failed disk drive.

A metadata file structure stored on each of a plurality of mirrored disk drives containing redundant copies of data units, the metadata file structure comprising a first and second set of n identifiers, wherein n is the number of mirrored disk drives and each identifier represents a mirrored disk drive, the first set of n identifiers indicating disk drives to be updated and the second set of identifiers indicating what disk drives contain current copies.

A program storage device, readable by a computer, tangibly embodying one or more programs of instructions executable by the computer to perform method steps for managing mirrored disk drives containing redundant copies of data, the method comprising the steps of:

• establishing a cohort set on each of the mirrored disk drives representing a status of the copies stored on the mirrored disk drives, the cohort set containing membership information for redundant copies of data units stored in the plurality of mirrored disk drives, the membership information comprising a data structure of 2n status bits for identifying which disks contain current copies of the data units, where n is the number of disks in the system, wherein the first n bits indicate an intention to update the membership information for the copies and the second n bits indicate a current state of the membership information;
• and
• updating the contents of the cohort sets when a disk drive failure has been detected to reflect unavailability of the copy of data on the failed disk drive.

A memory for storing data for managing mirrored disk drives containing redundant copies of data, comprising:

• a data structure stored in a memory of each of the mirrored disk drives, each of the data structure including a first and second set of n identifiers, wherein n is the number of mirrored disk drives and each identifier represents a mirrored disk drive, the first set of n identifiers indicating disk drives to be updated and the second set of identifiers indicating what disk drives contain current copies.