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Data resiliency on the cloud

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The major providers in the cloud space, such as Amazon, Rackspace, and IBM, include resiliency mechanisms that ensure data is not lost in the case of an infrastructure outage, at least to satisfy the levels of business continuity established in their service level agreements (SLAs). Some cloud providers also offer services that give users the ability to create private images, and snapshots of the instances and storage they provisioned for added safety from data loss. However, none of these prevent database outages. In addition, snapshots or images will save data only up to the point when the snapshot or image was created; data created or modified after that period is lost after the outage. Another issue to consider is data integrity and consistency. For example, taking a snapshot (for example, an Elastic Block Store (EBS) snapshot in Amazon), at a given time, might not necessarily ensure the data that has been snapshot is consistent. In DB2, the quiesce command is used to ensure the database is consistent, so a suggestion is to execute this command before a taking a snapshot.

The message of data reliability resonates well when explaining cloud concepts, but provides users a false sense of safety when working with their database. Users end up with the idea that database backups are not needed, and that mechanisms for high availability or disaster recovery are handled by the cloud provider.

Database backups and high availability and disaster recovery solutions, in conjunction with data resiliency mechanism from the cloud are needed to ensure minimal loss of data, and minimum outages.  For example, you might set up a process where you take online DB2 backups every hour, and create private images or snapshots at the end of each day.

From a high availability and disaster recovery perspective, you can use DB2’s HADR feature. With this feature, if the primary DB2 server goes down, workload will be automatically rerouted to the stand-by server in less than 10 seconds; therefore, a client might not notice any disruption in the system. Disaster recovery solutions are expensive because you need to rent or purchase not only hardware but a location in a separate vicinity. By using the cloud, the cost of setting up a disaster recovery site is drastically reduced. Simply choose a data center for your stand-by server that is in a location separate from your primary server.  You would still need to pay more because you are renting more resources from the cloud, but not as much as having another data recovery center for the company.

Data corruption either from a hardware malfunction, software malfunction, or user-error perspective can be somewhat handled by using database mechanisms, such as restoring the database prior to the time the corruption happened, and rolling forward the logs to the closest point in time prior to the corruption.

In summary, do not discount database backups, recovery, and high availability solutions of your database just because you are working on the cloud. Use these solutions in conjunction with cloud data resilience services for added safety from data loss.

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