When you replicate data (especially with databases) it's important that your blocks of data are in the same sequence. This is known as?
a. Synchronous replication
c. Write order fidelity
d. None of the above
Were you correct?
The correct answer is:
c) Write order fidelity
According to SAN expert Christopher Poelker, Write order fidelity is a term that describes the ability of d data replication hardware or software to move data between geographic locations while keeping consistency for transaction oriented applications. In other words, it's the ability to keep data "in the same sequence" as it was written at the originating source.
This is extremely important for database consistency. If data is written in an incorrect sequence at different sites, the transaction logs will no longer be consistent and databases can become corrupt at the remote site. The operations are kept in proper sequence by assigning either a timestamp or sequence number to each write at the source site. The data is then transmitted to the remote site over multiple links for load balancing or asynchronously for longer distances, then reordered to the proper time sequence before written to the logs at the remote site.