Difference between Synchronous & Asynchronous Replication [Table]

Posted by Anatoly Elberg

Aug 27, 2012 12:05:00 PM

Synchronous vs. Asynchronous ReplicationWhen a technician or server operator needs to create copies of data, be it over a SAN, LAN or WAN, there are two main methods of doing this. Synchronous and asynchronous replication each have their own benefits and drawbacks. Learn more about these two methods of copying data, so you can choose the right option for your needs.

Synchronous Replication

Essentially, synchronous replication writes the data to both the primary and to the secondary area at the same time. In doing this, the data remains completely current and identical. The process works quickly and there is a extremely small margin of error. Because of this, it is ideal for disaster recover and is the method preferred for projects that require absolutely no data loss.

Asynchronous replication

Asynchronous replication also writes data to both a primary and secondary site, however with this process there is a delay when data is copied from one to another. Experts call this approach to data backup, “store and forward”. With this type of replication the data first writes to the primary array and then commits the data for replication to a secondary source: either memory or disk-based. Finally, the data copies at scheduled intervals to the target. This method can work over longer distances than synchronous replication, so at times it may be the only option.

Synchronous vs. Asynchronous Comparison Table


Type of Replication



Recovery Point Objective


15 minutes to a few hours

Distance Limitations

Best if both SANs are in the same datacenter

Anywhere with a good data connection


Most expensive type of SAN solution

Not as expensive as Synchronous but more expensive than basic SANs.


What's Best for you?

Comparing the two types of replication, you can see there are certain projects more suited to one over the other. If a project must occur over long distances, asynchronous replication may be the only option. However, when precision is necessary, synchronous is the answer. Another comparison is cost and work involved. Generally setting up an asynchronous system costs less. The main thing to consider is exactly what your project needs. If zero data loss is a must, don't hesitate to choose synchronous replication. If your project does not require the precision and up-to-the-second accuracy of a synchronous replication system, the lower cost and ability to work over long distances of asynchronous replication is likely the best decision.

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Topics: Disaster Recovery

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