Expect the unexpected with a solid cloud DR strategy
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Cloud service providers thinking about adding Disaster Recovery as a Service (DRaaS) need to add terms like Recovery Point Objective, Recovery Time Objective, hot, warm and cold backup sites, and geographic diversity to their vocabularies. Here's a list of the essential terms:
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- Recovery point objective. An RPO is the targeted maximum amount of time that can be tolerated between mirroring your data. Some enterprises may require an RPO of zero, meaning they cannot lose any data. This requires continuous, synchronous replication. Other enterprises may be able to tolerate data gaps of seconds, minutes, hours or even days if they have to revert to a secondary site.
- Recovery time objective. An RTO is the target interval between when an application outage occurs and when the application must be back up and running. This includes the time it takes to detect the failure, prepare the backup site, initialize the failed application and perform any network configuration to reroute requests to the backup site. The lower the RTO, the shorter the time between disaster and recovery.
- Hot, warm and cold backup: A hot backup site typically houses mirrored standby servers that are always available to run an application after a disaster. This is an expensive option favored by enterprises with short RTOs and RPOs. A warm backup site generally keeps state up to date, but it takes additional time to bring online because the resources are not immediately available. A cold backup site often has an RPO of hours or days, and data is often replicated in increments of hours or days. It is a low-cost option for applications that do not require rigorous availability guarantees.
- Geographic diversity. Another key disaster recovery term, geographic diversity, is important because primary and backup sites should be distant enough from each other to minimize the possibility that a single disaster takes down both sites.
Which disaster recovery solution for the cloud?
According to a report by researchers at the University of Massachusetts and AT&T Labs, warm standby services are best suited for cloud disaster recovery services. "Cloud platforms can provide the greatest benefit to DR services that require warm standby replications," the report said. "In this case, the cloud can be used to cheaply maintain the state of an application using low cost resources under ordinary operating conditions. Only after a disaster occurs must a cloud-based DR service pay for the more powerful -- and expensive -- resources required to run the full application, and it can add these resources in a matter of seconds or minutes."
Note: This tip is a continuation from "Planning cloud disaster recovery services and avoiding the pain points."