Browse Prior Art Database

Data Recovery In Host Networks

IP.com Disclosure Number: IPCOM000049775D
Original Publication Date: 1982-Jul-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Hartung, MH: AUTHOR [+4]

Abstract

Subsystems require a mechanism for recovery in host networks (Fig. 1). Here, provision is made for reconstructing damaged data when an operating system fails.

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Data Recovery In Host Networks

Subsystems require a mechanism for recovery in host networks (Fig. 1). Here, provision is made for reconstructing damaged data when an operating system fails.

A network of hosts shares a storage subsystem. The subsystem provides storage capacity and access controls for program residence, data bases and temporary working storage on behalf of operating system and user routines running on the hosts. To facilitate data sharing, the subsystem provides two kinds of locks. A shared lock is required for data that is read but not changed; an exclusive lock is required for data that is changed.

Subsystems reset shared locks held by operating systems running on hosts that are reset. Exclusive locks are enforced until explicit commands indicate that partially updated data sets have been repaired, however. Reconstruction is supervised by a program running on any of the hosts in the network. Subsystems therefore associate locks with operating systems rather than hosts.

Data sets are stored in subsystem segments; the segements are made up of fixed length blocks. A block is addressed via its segment and block numbers. Segments 1-255 are reserved for operating system residence; blocks 0 of these segments receive dump information and blocks 1-255 are IPL (Initial Program Load) bootstrap routines. Segment 0 is null (i.e., empty).

Subsystems are "System Identifiers" (SID) to associate operating systems with hosts; there is an SID register for each host in the network. The SID value for an operating system is the number of its IPL segment. Subsystems also use a "System Register" (SR) with a bit corresponding to each IPL segment to track which operating systems are actively executing on hosts.

Hosts have IPL switches for selecting an IPL segment and a bootstrap routine. The host's IPL function transmits a reset signal and an IPL request to the subsystem. The request has three commands: (...