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Mirror Secondary Change Recording

IP.com Disclosure Number: IPCOM000243818D
Publication Date: 2015-Oct-19
Document File: 2 page(s) / 36K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a system for mirror secondary change recording, applied to disaster recovery systems, that allows clients to manipulate a mirrored relationship at the secondary level while maintaining the ability to re-synchronize (Resync) the mirror to ensure all changed tracks are copied.

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Mirror Secondary Change Recording

Processes in mirrored environments only monitor changes are at the primary location. If a client wants to use the secondary data, or even mistakenly uses the secondary data, the mirror becomes invalid. Additionally, clients have to purchase additional Direct Access Storage Devices (DASDs) to use as tertiary volumes to perform read/write operations

such as Disaster Recovery tests at a remote location, in order to preserve the mirrored environment.

The novel solution allows the clients to manipulate a mirrored relationship at the secondary level while maintaining the ability to re-synchronize (Resync) the mirror to ensure all changed tracks are copied. This system also reduces the need for the additional DASD so that Disaster Recovery tests can be performed directly against the secondary level.

This system utilizes existing hardware Change Recording technology on storage subsystems to track changes made to both the primary data and the secondary data. When primary data is changed, the system tracks those changes and then updates the changes to the secondary location on the next execution of the Resync. This solution introduces the use of change recording to the secondary data; the data at the primary must be copied over to the secondary in order to produce a complete copy at the time of the Resync. The combination of both primary and secondary recording ensures a 100% copy with the least amount of data transfer.

The solution introduces a new keyword during suspend processing of the mirror. For the purposes of this disclosure, the keyword is SECONDARYRECORDING (SECREC); however, for implementation, the actual keyword can be determined later. This keyword can be supplied via either command or parameter. When a suspend operation of the mirror is invoked with SECREC, Change Recording (an existing hardware (HW) feature) is turned ON for the secondary volumes associated with that session. The Change Recording feature on the box monitors the volumes for any writes to the secondary volumes, and then accordingly marks a bitmap. With Change Recording enabled, the client can use the secondary volumes for read/write purposes. As an example, a disaster recovery test can be performed to the secondary site while the mirror is suspended.

After the secondary devices are no longer needed for the read/write purposes, the system allows the client to Resync the mirror withou...