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Magic Mirror

IBM uses cross-site mirroring to protect your business-critical systems

IBM uses cross-site mirroring to protect your business-critical systems
Illustration by Nick Rotondo

Cross-site mirroring (XSM), as the name implies, is the act of mirroring across two sites. Those two sites could be two partitions on the same system or two systems separated by some distance. XSM is accomplished with the set of data-replication technologies available via PowerHA* for i. This article explains the different methods to perform XSM, along with their benefits and considerations. It also examines backup strategies that can be used within an XSM configuration.

Types of XSM

Under the XSM umbrella, three distinct flavors of data replication exist: geographic mirroring, Metro Mirror and Global Mirror. Within PowerHA for i, these technologies can be used to provide a complete high-availability (HA) solution, protecting your environment against planned and unplanned outages.

A base requirement for each is independent auxiliary storage pools (IASPs). By placing the application data and perhaps even the applications themselves within an IASP, you can perform seamless switchovers and failovers without an IPL on the backup node. XSM works by ensuring that each write to the IASP on the production node is also done on the backup node, either via IBM i storage management (geographic mirroring) or the Copy Services functionality on the System Storage* DS6000* or DS8000* systems (Metro Mirror or Global Mirror).

With geographic mirroring or Metro Mirror, the source and target are guaranteed to be in sync.

Jenny Dervin is an advisory software engineer for IBM. Jenny can be reached at jdervin@us.ibm.com.


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