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Before looking more closely at the cost factors of high availability (HA)—and why each has changed so significantly—it is helpful to first understand the concepts of recovery time objectives (RTO) and recovery-point objectives (RPO).
The graph in Figure 1 shows a variety of common System i business continuity technologies in which one axis indicates the time it takes to recover data after a failure/disaster (RTO), and the other axis indicates the completeness of data that is ultimately recovered (RPO). At the low end of the disaster recovery (DR) spectrum is tape backup (basic availability) and at the high end is high availability (HA)—a process more technically known as logical data replication-plus-switchover (LDR+Switch), which rapidly moves users and processes to a fully mirrored secondary server in order for it to assume all or most of the functions of the production server.
Unfortunately, the perception of many mid-size and small companies is that HA technology is so much more expensive than basic disaster recovery protection that it is considered “out of reach” in terms of both cost and complexity. But, in line with most other computing technologies, the range of options between the most basic DR protection and the high-end, fault tolerant, enterprise-scale solutions has increased and, overall, the cost of all the options has come down, radically in some cases.
High availability is certainly not “cheap” when you consider all of the components that are needed. What has changed is how the cost of each of these factors—each for its own reasons—has dropped. Here are the major components that contribute to the cost of an HA solution:
Hardware—A second System i server is needed, with enough capacity to accommodate the storage of replicated data and potential production demands. For instance, depending on how fully you want to run your applications from your backup environment during planned and unplanned downtime, this server may need to handle the same scale of transaction volumes and devices supported by the production machine. If less than full capability is acceptable during downtime, adjustments can be made. But in the end, a second server, ready to run, is a must.
Communication Bandwidth—If the second System i server is located off site, which is what is necessary to have true disaster recovery protection, then sufficient communication capacity (bandwidth) is needed to accommodate the amount of data flowing to it from the production machine. This includes the I/O processing capacity of the backup server and the communication lines between sites.
High Availability Software—This component executes, manages, and monitors the replication or mirroring of designated business-critical data to the backup server. It also provides the ability to efficiently move users and processes to the backup server during downtime events. In addition to the initial purchase cost for this software, annual maintenance contracts and installation and training costs must be considered.
High Availability Management—As with any other infrastructure software or system, some level of staff time is required each day to monitor and manage the data replication processes to ensure that the mirrored data is accurate and usable when needed. In part, the amount of time needed for this task depends on the scale of your environment. But the self-managing capabilities of the HA software can have an even bigger impact. Even large scale HA environments can be easy to manage, with the right software.
So what has changed? Why should you re-consider whether you can justify investment in a true high availability solution? Here are five reasons:
Reason #1 – Decreasing Cost of Hardware
It’s no secret System i machines pack a lot of bang for the buck, and the current configurations and pricing models of the System i make buying a second machine for high availability significantly less costly than it was, even just a few years ago. If you intend to replicate data only for disaster recovery purposes (not to run applications during downtime on the backup machine but only to be able to retrieve the data from it), an economical option is to buy a smaller System i model with enough power to handle replication. This at least keeps your “backup” current and on-disk, not just on tape.
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