Secondary logging is an advanced feature that improves replication performance throughput. This feature uses the Secondary SRL to stage the data before writing to the data volume. The data volume write requires write-order fidelity, which slows the replication throughput. Staging the data to the Secondary SRL allows an immediate acknowledgment of the data write, and allows the Primary to push more data. The Secondary applies the data to the volume in a parallel manner to maintain write-order fidelity. The data acknowledgment is performed immediately after writing on the SRL.
The requirements for automatically enabling support for Secondary logging are as follows:
The Primary SRL and the Secondary SRL volumes must be of the same size. The SRL can be resized using the vradmin resizesrl command.
The RVG version on both the Primary and the Secondary must be 40 or above. The vxprint -Vl command displays the RVG version. The vxrvg -g diskgroup upgrade rvg command can be used to upgrade the RVG version. The RVG version can be upgraded only when the RLINK is up to date.
The disk group version on both the Primary and the Secondary must be 170 or above. The vxdg list diskgroup command displays the disk group version. The vxdg upgrade diskgroup command can be used to upgrade the disk group version. Upgrading the disk group using this command automatically upgrades the RVG versions of all the RVG's in the diskgroup. Note that before upgrading the disk group, it is recommended that you pause the replication prior to the upgrade, and resume replication after the upgrade. The RLINK needs to be up to date, otherwise only the disk group will be upgraded, and the RVG upgrade will fail.
If any of these requirements are not met, the Secondary logging feature is automatically disabled, and traditional replication is used, which may provide lesser replication throughput.