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Disaster Recovery and the CloudDECEMBER 1, 2010 BY MICHAEL LYLE 2 COMMENTS
It goes without saying that modern business relies on information technology. As a result, it is essential thatoperations personnel consider the business impact of outages and plan accordingly. As an illustration, Virgin Bluerecently experienced a twenty-hour outage in its reservation system that resulted in losses of up to $20 milliondollars. The cloud provides both considerable opportunities and significant challenges relating to disaster recovery.
In general, organizations must currently build multiple levels of redundancy into their systems to reach high-availability targets and to protect themselves from catastrophic outages during a natural or man-made disaster. Adisaster recovery strategy requires that data and critical application infrastructure be duplicated at a separatelocation, away from the primary datacenter. Cutting over to a disaster recovery site is usually not instantaneous andredundancy is often lost during the contingency operating plan. For this reason, site-local redundancy mechanisms– such as high availability network systems, failover for portions of the application stack, and SAN-level redundancyare also required to achieve availability goals. Public clouds often further complicate disaster recovery planning, asthe organization’s critical systems may now be spread across their own infrastructure and a multitude of outsidevendors, each with their own data model and recovery practices.
Business requirements and application criticality should guide the approach chosen for business continuity. Consider the concepts of RPO (Recovery Point Objective) and RTO (Recovery Time Objective). The RPO of a systemis the specified amount of data that may be lost in the event of a failure, while the RTO of a system is the amount oftime that it will take to bring the system back online after a failure. In general, site-local mechanisms will providenear-instantaneous RPO and RTO, while disaster recovery systems often will have an RPO of several hours or daysof information, and an RTO measured in tens of minutes. Through increasingly sophisticated (and costly)infrastructures, these times can be reduced but not entirely eliminated.
Illustration of RTO and RPO in a backup system
Dedicated redundancy infrastructure, both site-local and for disaster recovery purposes, must be regularly tested. Additionally, it is essential to ensure that the disaster recovery environment is compatible with the existinginfrastructure and capable of running the critical application. This is an area where change managementprocedures are important, to ensure that critical changes to the production infrastructure are made in the standbyenvironment as well. Otherwise, the standby environment may not be able to correctly run the application when thedisaster recovery plan is activated.
The primary factor that determines RTO and RPO is the approach used to move data to the contingency site. Theeasiest and lowest cost approach is tape backup. In this case, the RPO is the time between successive backupsmoved off-site (perhaps a week or more) and the RTO is the amount of time necessary to retrieve the backups,restore the backups, and activate the contingency site. This may be a significant amount of time, especially ifpersonnel are not readily available during the disaster scenario. Alternatively, a hot contingency site may bemaintained, and database log-shipping or volume snapshotting/replication can be used to send business data tothe secondary site. These systems are costly, but readily attain an RTO of under an hour, and an RPO of perhapsone day. With substantial investment and complexity, RPO can even be reduced to the range of minutes. However,organizations have often been surprised to find that the infrastructure doesn’t work when it is called upon, oftenbecause of the complexity of the infrastructure and the difficulties involved in testing a standby site.
When procuring IaaS (Infrastructure as a Service) or SaaS (Software as a Service), it is essential for the organizationto perform due diligence regarding what disaster recovery mechanisms the service vendor uses. The stakes are
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too high to trust service level agreements alone (in the case of a catastrophic failure during a disaster, will thevendor be solvent and will the compensation received be sufficient to compensate for business losses?).
Disaster Recovery as a Service, or DRaaS, is an emerging category for organizations that wish to control their owninfrastructure but not maintain the disaster recovery systems themselves. With a DRaaS offering, an IT organizationdoes not directly build a contingency site, but instead relies on a vendor to do so on a dedicated or utility computinginfrastructure. The cloud’s advantages in elasticity and cost-reduction are significant benefits in a disaster recoveryscenario, and service offerings allow organizations to outsource portions of contingency planning to vendors withexpertise in the area. However, many of the complexities remain and it is essential to perform the due diligence toensure that the contingency plan will work and provide a sufficient level of service if called upon.
Finally, there are emerging technologies that combine site-local redundancy and disaster recovery into a unifiedsystem. For example, distributed synchronous multi-master databases allow an application to be spread acrossmultiple locations, including cloud availability zones, with the application active and processing transactions in all ofthem. A specified portion of the system can be lost without any downtime or recovery effort. These emergingsystems offer the prospect of dramatically reducing costs and minimizing the risk of contingency sites notfunctioning properly.
About the Author
Michael Lyle (@MPLyle) is CTO and co-founder of Translattice, and is responsible for the company’s strategictechnical direction. He is a recognized leader in developing new technologies and has extensive experience indatacenter operations and distributed systems.
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Related posts:
1. Redundancy in Data Storage: Part 2: Geographical Replication2. OTV and Vplex: Plumbing for Disaster Avoidance3. How to Boost Cloud Reliability4. Business Drivers for Cloud Infrastructures5. Building a Hybrid Cloud
FILED UNDER: CONCEPTS TAGGED WITH: DATA CENTER, DISASTER RECOVERY, DR
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Tweets that mention Disaster Recovery and the Cloud — Define The Cloud -- Topsy.com says:December 1, 2010 at 12:49 pm
[...] This post was mentioned on Twitter by Joe Onisick, Michael Lyle. Michael Lyle said: I'm now contributing to@jonisick 's Define the Cloud. My first post: http://www.definethecloud.net/disaster-recovery-and-the-cloud [...]
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Redundancy in Data Storage: Part 1: RAID Levels — Define The Cloud says:February 21, 2011 at 12:03 am
[...] I think Joe raises a good point, and this is a natural topic to dissect in detail after my previous article aboutcloud disaster recovery and business continuity. I, too, am concerned by the variety of data redundancyarchitectures used in enterprise [...]
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