Why Use Replication? (page 1 of 3)

It used to be that running a daily backup was the only protection required, but as internal employees, partners and customers exceedingly rely on access to these systems around the clock, providing higher levels of protection becomes vital.

Replication is the only technology that can satisfy the needs of the most demanding systems, as only replication can provide instant access to data and zero data loss (minimal Recovery Point Objective or RPO and minimal Recovery Time Objective or RTO).

Replication is simply the process of copying data from one location to another, but there are many ways in which this can be done and this article will explore some of these ways.


Figure 1: Data loss (Recovery Point Objective) and Downtime (Recovery Time Objective)

Backup is still the cornerstone of a solid disaster recovery strategy, but since backups are usually run only once a day there is a high risk of losing large amounts of data and also having systems being offline for long periods of time (the Recovery Point Objective and Recovery Time Objective for backup is usually days, whereas with replication it is usually minutes or seconds).

With replication, none of these risks exist, but a comprehensive disaster recovery strategy should not only use replication as the sole means of protecting data as there are some disadvantages of doing so. For example, if a virus enters the system and only replication is used to protect data then that virus will most likely be replicated along with all the rest of the data to the secondary location.

That is why backup should still be used as it is a point-in-time copy of data on tape in a safe location that can be restored without viruses or data corruption.

Using replication (especially in real-time) for 100% of data in an environment is unrealistic and cost-prohibitive. The bandwidth required for most businesses wanting to replicate all data would be astronomical, besides the fact that all data is not created equal so it would not make sense to replicate everything. Rather consider these kinds of systems:

• Customer-centric systems: All data stored in systems being accessed by customers is mission-critical and should be protected at all costs.

• Partner-centric systems: Most of the data stored in partner-centric systems is business-critical, but not all. Carefully consider what should be replicated and what should only be backed up.

• Internal systems: Certain internal systems are critical for keeping the business going, such as e-mail, and should be protected at all costs. Other functions might accept a day or more worth of data loss.

Different Ways of Replicating
When it comes to replicating data there are many ways in which this can be done and many technologies used to do so. When choosing the right method of replication, carefully consider the data that is being protected and how much of that data you can afford to lose. The different methods are:

• Synchronous Replication: Data is copied in real-time from system to system, so if the primary system was to fail the secondary system has an exact copy of data and can take over instantaneously. Synchronous replication is the only method that guarantees zero data loss.

• Asynchronous Replication: Data is copied from system to system with a small lag time, usually measured in milliseconds.