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Consistency of disaster recovery data, part of which is copied by cascading synchronous and asynchronous disk copy and other part of which is only copied by asynchronous disk copy, at the time of synchronous disk copy failure.

IP.com Disclosure Number: IPCOM000235743D
Publication Date: 2014-Mar-25
Document File: 2 page(s) / 35K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method to maintan consistency of data copied by the mixture of cascading synchronous plus asynchronous disk copy and asynchronous disk copy at the failure of synchronous disk copy.

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Consistency of disaster recovery data, part of which is copied by cascading synchronous and asynchronous disk copy and other part of which is only copied by asynchronous disk copy, at the time of synchronous disk copy failure.

Disclosed is a method to maintan consistency of data copied by the mixture of cascading synchronous plus asynchronous disk copy and asynchronous disk copy at the failure of synchronous disk copy.

Background

In computer system environments, a copy by disk subsystem (disk copy) is often used to copy data written by a server from one disk subsystem to another disk subsystem. While there are many methods to maintain consistency of asynchronous disk copy, consistency of synchronous disk relies on the nature of synchronous copy. A method to maintain consistency of synchronous disk copy already exists, and it is applicable to cascading synchronous plus asynchronous disk copy, too. But, the existing method is not enough to maintain consistency of data copied by the mixture of cascading synchronous plus asynchronous disk copy and asynchronous disk copy. This invention addresses this issue.


1. Existing method

When synchronous disk copy fails, it is necessary to use the following procedure to maintain consistency of copied data (see US Patent 6199074).

(1) Server instructs disk subsystem to hold I/O operations temporarily and suspend all synchronous disk copy

(2) Server instructs disk subsystem to resume I/O operations

This method can also be used for cascading synchronous plus asynchronous disk copy, which consists of serially connected synchronous disk copy and asynchronous disk copy. Because there are various method to maintain consistency of asynchronous disk copy, data copied by cascading synchronous plus asynchronous disk copy is consistent if data copied by synchronous copy is consistent at...