Patent ID: 6199074
Filing Date: 2001-03-06
Classification: G06F,Y10S

Abstract:
A method for maintaining backup data in a database management system (DBMS) including at least one primary controller, multiple primary data storage devices each coupled to one of the primary controllers, multiple secondary data storage devices each coupled to one of multiple secondary controllers, each secondary controller being coupled to one of the primary controllers, wherein one or more primary databases reside on the primary data storage devices and a corresponding number of secondary databases reside on the secondary data storage devices, wherein the DBMS updates each secondary database to mirror its corresponding primary database, each corresponding primary and secondary database together constituting a mirrored pair, the method comprising:at a first time, detecting unavailability of a first database for read/writes, said first database being a member of a first mirrored pair including the first database and a counterpart database;identifying all primary and secondary data storage devices containing any data of the first mirrored pair of databases, said identified primary and secondary data storage devices constituting affected primary and secondary devices;discontinuing all read/write operations by the affected primary devices ongoing at the first time, also preventing future read/write by the affected primary devices;instructing each secondary controller coupled to any affected secondary devices to terminate updating of the affected secondary devices;detecting termination of updating by the secondary controllers, and in response thereto, resuming read/writes with the affected primary devices;each primary controller coupled to affected primary devices receiving changes to the primary database of the first mirrored pair, and in response thereto, logging the received changes;detecting removal of the suspending condition, and in response thereto, resynchronizing the secondary database of the mirrored pair by:applying the logged changes to the secondary devices containing the secondary database of the mirrored pair; andinstructing the secondary controllers to resume updating of the secondary database of the mirrored pair to mirror its corresponding primary database.