Informing the IBM Community

IBM i: Reflections on Mirroring


Every organisation running its core business on IBM i, regardless of size, must be able to keep its system and business application up and running during planned and unplanned outages, caused by events like application failure, data corruption, power outage or extreme weather events. Depending on the criticality and size of the business, some organisations are required to have a solution which will switch automatically to the backup system and requires zero loss of data.

In order, to achieve this many IBM i customers rely on third party vendor, software replication solution based on the concept of remote journaling, which requires constant monitoring and skilled IT personnel to maintain a switch ready environment.

IBM provides complete and integrated DR and high availability solution, called IBM PowerHA SysteMirror for i. IBM PowerHA for i provides local and remote high availability solutions to protect against either planned or unplanned outages and can also provide solutions for disaster recovery and offline backups in an easy and simplistic for managing, way.

PowerHA leverages the usage of IBM SAN storage technologies based on IBM Storwize and Enterprise DS and FlashSystems storage arrays.

They include technologies like Metro Mirror(synchronous replication), Global Mirror(asynchronous replication) and FlashCopy. FlashCopy is especially interesting for IBM I customers, since it can eliminate all backup downtime.

PowerHA for i is also enabled for customers using internal storage, using Geographic mirroring technology. Using Geographic mirroring, IBM i OS handles the replication at a disk page level, using the TCP/IP stack in the License Internal Code to leverage the transfer of the data to the backup system.

The PowerHA solution is designed to fit small to midsized businesses (SMBs) as well as large enterprises. Doesn’t matter if the backup system is located in a few miles or hundreds of miles from the primary system, there’s a PowerHA solution that will support all types of IBM i customers.

PowerHA for i technology uses the concept of independent auxiliary storage pool (iASP), which is effectively a pool of disks which is separate and independent from SYSBAS. The concept is well known in the UNIX/AIX world as logical volumes, but it’s still not very popular among IBM i customers due to the perception that it requires significant effort, in order to enable the business applications to use it.

The iASP is a volume group of disks that can be connected to more than one system, can be taken offline or online without a system IPL and can be switched between the nodes in PowerHA cluster.Effectively taking the iASP offline and online is a mini IPL, since the iASP contains a separate namespace and DB2, but the process is much quicker than a full system IPL.

“In its most basic form, shared storage clustering is about switching access to the shared disk pool between systems, so if system A goes away, system B takes over the data and production. The PowerHA basic architectural construct isn’t based on replication—although most of our clients replicate the IASP data. PowerHA is about sharing storage between systems.”

Steven Finnes,Worldwide ide offering manager for IBM Power Systems High Availability solutions. 

In a typical iASP implementation, the application and all of the data are located within the iASP, which then gets replicated to the backup site. Since the solution is highly integrated and requires minimal effort for monitoring and managing, with one command, production workloads can be switched from the primary node to the secondary node. It even is configured to perform switch automatically and sometimes the user is not even aware that a switch has occurred.

With the various replication technologies, available within PowerHA SystemMirror for i, maintenance and monitoring of your high availability environment can be simple and pain-free. Many customers using PowerHA SystemMirror switch from production to backup regularly, giving them added confidence in their disaster recovery plans.

About the author:
Tsetso Marinov is an IBM POWER, IBM i and IBM Storage technical consultant, specialising in external storage virtualization, PowerVM VIOS and PowerHA for i.  Prior to joining Northdoor in 2015, Tsetso worked in numerous end user IBM i teams including a large high street bank where he was involved in managing large Enterprise POWER servers and DS8000 storage.


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