PRO vs RTO

source : http://www.druva.com/blog/understanding-rpo-and-rto/

Recovery Point Objective (RPO) and Recovery Time Objective (RTO) are one of the most important parameters of a disaster recovery or data protection plan. These objectives guide the enterprises to choose a optimal data backup (rather restore) plan.

RPO: Recovery Point Objective

Recovery Point Objective (RPO) describes the interval of time that might pass during a disruption before the quantity of data lost during that period exceeds the Business Continuity Plan's maximum allowable threshold or "tolerance."

Example: If the last available good copy of data upon an outage is from 18 hours ago, and the RPO for this business is 20 hours then we are still within the parameters of the Business Continuity Plan's RPO. In other words it the answers the question - "Up to what point in time could theBusiness Process's recovery proceed tolerably given the volume of data lost during that interval?"

RTO: Recovery Time Objectives

The Recovery Time Objective (RTO) is the duration of time and a service level within which a business process must be restored after a disaster in order to avoid unacceptable consequences associated with a break in continuity.

In other words the RTO is the answer to the question: "How much time did you take to recovery after notification of business process disruption?"

At first glance these two terms appear to be quite similar. The best way to understand the difference between them is to associate the "RP" in "RPO" by imagining that they stand for "Rewrite Parameters" and the "RT" in "RTO" as "Real Time."

RPO designates the variable amount of data that will be lost or will have to be re-entered during network downtime. RTO designates the amount of "real time" that can pass before the disruption begins to seriously & unacceptably impede the flow of normal business operations.

The RTO/RPO and the results of the Business Impact Analysis (BIA) in its entirety provide the basis for identifying and analyzing viable strategies for inclusion in the business continuity plan. Viable strategy options would include any which would enable resumption of a business process in a time frame at or near the RTO/RPO. This would include alternate or manual workaround procedures and would not necessarily require computer systems to meet the objectives.

There is always a gap between the actuals (RTA/RPA) and objectives introduced by various manual and automated steps to bring the business application up. These actuals can only be exposed by disaster and business disruption rehearsals.

Some Examples

Traditional Backups: In traditional tape backups, if your backup plan takes 2 hours for a scheduled backup at 0600 hours and 1800 hours, then a primary site failure at 1400 hrs would leave you with an option to restore from 0600 hrs backup which means RPA of 8 hours and 2 hours RTA.

Continuous Replication: Replication provides higher RPO guarantees as the target system contains the mirrored image of the source. The RPA values depend upon how fast the changes are applied and if the replication is synchronous or asynchronous. RPO is dependent on the fact that how soon can the data on target/replicated site be made available to the application.

Druvaa Replicator

Druvaa Replicator is Continuous Data Protection and Replication (CDP-R) product which near-synchronously and non-disruptively replicates changes on production sever to target site and provides point-in-time snapshots for instant data access.

The partial synchronous replication ensures that the data is written to a local or remote cache (caching server) before it application can write locally. This ensures up to 5 sec RPO guarantees. CDP technology (still beta) enables up to 1024 snapshots (beta) at that target storage which helps the admin to access current or any past point-in-time consistent image of data instantly, ensuring under 2 sec RTO.

reference : 

https://www.netiq.com/documentation/noc50/server_installation/data/bmg3ki6.html

http://searchdisasterrecovery.techtarget.com/essentialguide/Essential-guide-to-business-continuity-and-disaster-recovery-plans#guideSection1

https://technet.microsoft.com/en-us/library/cc263031.aspx