Shared storage controller for dual copy shared data

Abstract

A computing system constructed of multiple processing elements containing private storage, attached to a shared global storage, is called a closely-coupled system. Each processing element may be a single processing unit (PU) with private storage, or a tightly coupled multi-processor unit with private storage. Either type of processing element will be referred to as a Central Processor Complex (CPC), the computing system complex as a whole is referred to as a sysplex. IBM ESA/390 processors provide examples of both single and multi-processor CPC's. For a highly-available shared storage for data-sharing in a multi-processing element environment, highly-available shared storage is provided by a duplexed controllers with non-volatile storage, which is accessed by tightly connected Processing Elements as a single logical copy. Our duplexed controllers provide not only the shared data but also the control information necessary for multi-Processing Element data management with speed-matching processor. The duplexed controllers, including a primary and backup controller, are always synchronized to execute each message command to ensure that they do not diverge. Each controller of the duplexed controller receives its own command from a Processing Element and reaches consensus with other controller to synchronize command execution and return a response code to the Processing Element. To sequence and synchronize the command execution by each of the duplexed controller, a tightly-synchronized Sysplex timer is used to time-stamp each command and response so that the duplexed controllers will run in synchronism. When an 'out of sync' condition is detected by a SSC, the monitoring information of SSC and integrated SP, and the result of diagnostics are used to determine the faulty SSC of a the duplexed SSC.