Abstract: A method for updating mass storage device configuration records during a configuration change within a computer system is disclosed. A unit configuration record is stored in a system mass storage device. The unit configuration record is unique to each system and it includes a configuration identification, a sequence number and an alteration count table. In addition, a logical device identifier is stored in each mass storage unit within the system. The logical device identifier is unique to each mass storage device unit and it includes a configuration identification, a unit number and an alteration count. If a configuration update is necessary, the corresponding alteration count of the unit configuration record is first incremented, a new logical device identifier is then built with the new alteration count, and finally the new logical device identifier is written to a mass storage device that requires update.

Abstract: A data processing system having a pair of mirrored storage units maintains a state record of the mirrored pair in system memory. In order to be able to determine state when the system is re-initialized, this state information is also stored on each storage unit of the mirrored pair, and in an alternate location. When the state changes, the operating system writes the new state to those storage units which are still functioning, and to the alternate location. In order to prevent ambiguous situations, only certain defined state transitions are permitted. When the system is re-initialized, it attempts to read the state information stored on the storage units. If either unit can not be read, the system substitutes the state retrieved from the alternate state record for the state that would have been read from the non-responding unit. This pair of states from the two units index an unique entry in a state derivation table containing the resultant state.

Abstract: A method of pairing disk units in a computer system where mirroring is desirable is disclosed. Where possible, disk units are paired with other disk units located on a different bus. This provides the highest level of protection against inaccessible data due to data loss or failure of a component in the computer system. Where this is not possible, the remaining disk units are paired with disk units located on a different I/O processor, a different controller, or a different disk enclosure. Where none of these pairings are possible, the remaining disk units fall below the threshold level of protection and therefore cannot be paired within the segment. Any disk units that could not be paired are placed on a spare list. Several attempts are made to pair up disk units on the spare list. If all of these attempts fail, the paired disk units with the lowest level of protection are broken apart and added to the spare list, where attempts are again made to pair up the disk units on the spare list.

Abstract: A method of pairing disk units in a computer system where mirroring is desirable is disclosed. Where possible, disk units are paired with other disk units located on a different bus. This provides the highest level of protection against inaccessible data due to data loss or failure of a component in the computer system. Where this is not possible, the remaining disk units are paired with disk units located on a different I/O processor, a different controller, or a different disk enclosure. Where none of these pairings are possible, the remaining disk units fall below the threshold level of protection and therefore cannot be paired within the segment. Any disk units that could not be paired are placed on a spare list. The paired disk units with the lowest level of protection are broken apart and added to the spare list, where attempts are again made to pair up the disk units on the spare list.