The selection between synchronous or asynchronous mode is made according to the RPO/RTO ratio (described in the following paragraph), the distance and the level of availability desired. The quality of link between the sites should also be considered.

Tolerance / Criticality of the Application Data Protection strategy
RTO more than or equal to 72 hours Restoration from backups on tape
RTO less than 24 hours Restoration from a remote site, asynchronous replication
nul RPO / minimum RTO Restoration from a remote site, synchronous replication
nul RPO/ metropolitan distance Synchronous replication
nul RPO / departmental distance Synchronous replication between both departmental sites and asynchronous replication between departmental sites and non-departmental sites

The replication technologies can be applied at the storage level; replication is performed between two remote disk arrays connected through Fiber Channel (FC) technology, but it is also possible to perform a data replication through conventional TCP/IP network.

  • Mirroring or Cloning

In synchonous mode, this technology provides an identical copy of the production volume, it is generally used for disaster recovery on another site, for tests or backup on a remote server executed from production data.

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