James Michael Showalter

Coordinated resource recovery in VM/ESA

A system service for coordinated recovery of resources is a critical function needed for distributed processing environments because applications need to provide for data integrity while the location of the data and processes are transparent to the application. VM is the first IBM operating system to provide Coordinated Resource Recovery as a system service rather than as a service provided by unique environments running on the operating system, and the VM Common Programming Interface-Communications and Shared File System are the first subsystems to utilize the service. This paper is an overview of why and how VM provided Coordinated Resource Recovery (CRR). CRR is the implementation of the Systems Application Architecture™ (SAA™) resource recovery interface within Virtual Machine/ Enterprise Systems Architecture™ (VM/ESA™). This coordinated sync point system service allows one or more applications or subsystems to update multiple resources and to request that all updates be committed or backed out together. The applications and their respective resources can be local or distributed. CRR either coordinates the request to commit or backout immediately, or supports automatic resource resynchronization in case a system or subsystem fails. When restart is not possible, CRR allows for intervention by a system operator or administrator.

VM/ESA support for coordinated recovery of files

This paper discusses the concepts and facilities of the Shared File System (SFS) support for Virtual Machine/Enterprise Systems Architecture™ (VM/ESA™) Coordinated Resource Recovery (CRR). It includes background information on limitations that lead to SFS support for coordination of file recovery functions. The level of support provided by the Virtual Machine/System Product (VM/SP) Release 6 SFS support is identified and contrasted with the support provided in VM/ESA. The paper contains an overview of the system structure and the rationale for the support and is a discussion from the overall perspective of the total system environment and system processing for resource recovery. After the concepts and structure of VM/ESA SFS support are introduced, the paper discusses the specific technology involved in providing SFS support for Coordinated Resource Recovery. This includes a discussion of specific facilities used by SFS and how SFS deals with certain conditions that can arise. In addition, this paper discusses the Conversational Monitor System (CMS) compatibility considerations that contributed to the design of SFS support for Coordinated Resource Recovery. This includes compatibility with prior releases and compatibility with the CMS file system support for minidisks. Finally, some of the future directions for file system support of resource recovery are identified along with some of the challenges that remain to be solved.