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Synchronous vs. asynchronous

Where can I find a detailed comparison matrix for synchronous vs. asynchronous replication and the benefits and disadvantages of each technology?

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Veritas has a white paper on this, but it doesn't have a chart comparing them.

Asynchronous replication does not depend on acknowledging the remote write, but it does (in Veritas' implementation) write to a local log file. Synchronous replication depends on receiving an ACK from the remote system and the remote system also keeps a log file.

Async is fastest. It is impossible to accurately recreate data at the remote end because there is no way of knowing what was successfully transmitted. However, if there is a disaster at the local site, data will need to be rebuilt from the log file. If the local log file is gone, then traditional backup/recovery is needed.

If synchronous replication is used the remote site data could be used to rebuild data at the local site. In that sense, synchronous replication is more secure by providing additional redundancy.

Regards, 

Marc

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This was first published in April 2002

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