In my earlier post, I defined the differences between high availability (HA) and disaster recovery (DR). I noted that in designing for DR, you want to build your secondary system so it will survive a large or widespread event, such as a hurricane, earthquake or meteor strike while being less concerned about failover time.
Recall that a true DR solution needs to address entire systems, not just individual components. In this blog, I’ll discuss how SharePlex® can be used to support Oracle database recovery as a part of a complete disaster recovery plan.
Disaster Recovery for Oracle Databases
Oracle offers several disaster recovery solutions, including DataGuard and Global Data Services. However, these have some significant limitations and requirements that need to be considered when creating a disaster recovery plan. Also, these solutions require additional maintenance and configuration, and can require additional license costs.
Oracle DataGuard
Oracle DataGuard maintains a secondary copy of your primary database by copying (or “shipping”) the contents of the redo log from the primary to the secondary. This definitely achieves one of the basic goals of disaster recovery, with limitations.
DataGuard has many configuration options and settings. Not only does this add complexity; but some of the options that are best for DR, such as immediate shipping of transactions without waiting for a log switch, are only available at extra cost or with Oracle Enterprise Edition.
One critical limitation is that DataGuard can only be used between the same major versions of Oracle. So, if you have an Oracle 11 database and want to upgrade to Oracle 12, you must upgrade both your primary and secondary databases; and until both databases are upgraded, at best your DR database will be behind your primary database.
Oracle Global Data Services
Oracle Global Data Services combines DataGuard with Oracle GoldenGate and other components in a system that guarantees availability of your data for both DR and HA. However, this comes at significant cost. First, it’s only available for Oracle Enterprise Edition, and requires licensing both additional DataGuard features and Oracle GoldenGate.
The Alternative – SharePlex
For disaster recovery, SharePlex can help you overcome many of the limitations and issues with DataGuard, at a significantly lower cost than Global Data Services.
Like DataGuard, SharePlex moves data from a source (primary) database to a target (secondary) database. Unlike DataGuard, SharePlex moves records from the source to the target as soon as they appear in the redo log. This significantly reduces the possibility for data loss and at the same time ensures a more even load on your network.
SharePlex is asynchronous, which means that your source database is never held up waiting on a transaction to be written to the target. While in certain circumstances, this can result in the loss of a few committed transactions, the higher performance provided often offsets this risk.
Almost without exception, users tell us that SharePlex is significantly easier to configure and maintain than DataGuard or Oracle Data Services.
SharePlex can be used across versions and editions of Oracle. This can mean no loss in protection in the case of version upgrades, and allow for DR systems to be less robust than their production counterparts.
Finally, the SharePlex copy is fully open for read and write, and so can be used for reporting. Moving reporting to the database instance also used for disaster recovery can often allow postponement of hardware upgrades.