High Availability for IBM i

High Availability / Disaster Recovery
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

A technical review of software and hardware-based solutions.


Editor's Note: This article is an extract of the white paper High Availability for IBM i available free from the MC White Paper Center. 


This article describes what you need to know in order to make an informed decision with regard to IBM i high availability strategies so that your business requirements for recovery time objective (RTO) and recovery point objective (RPO) are not compromised. With the advent of the unified Power Systems platform, common storage platforms, and virtualization, maintaining high availability protection for an IBM i environment requires careful thought and clear understanding of its underlying architecture and technologies.


On the IBM i platform, there are fundamentally two ways to protect your business from unplanned business outages due to server failure:


1. Logical replication to maintain a hot backup copy of the environment that is fully available to the business at the point of switchover


2. Hardware HA to maintain an offline backup copy of the environment that is ready and waiting to reconstruct the environment with the latest possible copy of the data


Both approaches are strategic for IBM i and Power Systems hardware, and both have advantages as well as challenges that must be overcome in order to meet the goals of no loss of data (RPO) and the fastest possible recovery (RTO).


Logical replication is the term used in this article to define journal-based data resiliency. Every change to the data is logged, sent to the backup system, and immediately applied there. The OS journal function ensures that the journal record reflects the most recent state of the data.


The IBM i remote journaling feature ensures the data is securely written to the backup system so that the best possible RPO is achieved, while RTO will depend upon how quickly the high availability solution applies those journaled transactions, in the correct order, to the production database on the backup system.


Hardware HA is the term used in this article to define the disk-based replication native to the IBM TotalStorage SAN system, which employs sector-based replication capability between two SAN environments. The IBM i single-level store memory architecture employs a memory-page-based system that maps to a string of disk sectors. When the memory page is written to disk, the first SAN makes a sector-by-sector copy on the second SAN. In order to preserve the unique architecture of IBM i—which treats memory and disk storage as one—the data being copied is encapsulated and treated as a special subset of the system address range. This encapsulation becomes the basis for many possible data resiliency choices from which to choose. As such, in this article, we will also treat IBM i-based XSM geographic mirror technology as a hardware HA solution.


Want to learn more? Download the complete white paper High Availability for IBM i from the MC White Paper Center.

as/400, os/400, iseries, system i, i5/os, ibm i, power systems, 6.1, 7.1, V7, V6R1