AIX > Administrator > High Availability

Defining Availability

When discussing availability, most of us think of issues that relate to disaster recovery and failover. However, the general meaning of "availability" encompasses far more than this. According to, the definition of availability is:

1. Present and ready for use; at hand; accessible

2. Capable of being gotten

3. Qualified and willing to be of service or assistance

This definition fits well with the IBM On Demand Business initiative and, specifically, the Capacity on Demand (CoD) and Capacity BackUp offerings for IBM* eServer pSeries* and eServer p5 servers. In this article, I'll explain these features and ways to apply them.

Planning for Growth

CoD allows you to have additional processors and memory configured in the system but only pay for the extra resources when you start using them. There are several flavors of this capacity, and they each work a little differently, as I'll explain later. CoD's purpose is to help ensure the resources are there when they're needed as the workload grows. Two of the key advantages to implementing CoD are:

1. The resources are already there, so no disruptive installations are needed to activate them.

2. Spare processors in the system are used for dynamic processor sparing. This means that if a processor starts to fail, it's deactivated and one of the CoD processors is activated in its place.

So, not only do you have the capability to grow into the capacity, but it's also provided in a seamless, non-disruptive manner and can be used to provide failover for processors. 

CoD comes in four flavors--Capacity Upgrade on Demand (CUoD), On/Off CoD, Reserve CoD and Trial CoD. Capacity Backup for Disaster Recovery is an additional offering.

Take advantage of the capacity offerings IBM has to facilitate business continutity. Availability can grow as your business grows.

Jaqui Lynch is an independent consultant, focusing on enterprise architecture, performance and delivery on Power Systems with AIX and Linux.

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