Using SIOS DataKeeper in a WAN environment requires special configuration due to the nature of WAN networking. The following tips are recommended:
- To prevent false failover, you should enable manual failover confirmation. Because most WANs are somewhat less reliable than LANs and because typical WAN mirror configurations will have only one comm path, this is usually a good idea. With this option enabled, a LifeKeeper failover will proceed only if the user confirms the failover by using the lk_confirmso command. Refer to the lk_confirmso man page for more details.
- Determine the proper value for LKDR_ASYNC_LIMIT , based upon the latency and throughput of the WAN. The LKDR_ASYNC_LIMIT parameter (which is set in /etc/default/LifeKeeper) determines the number of outstanding asynchronous write operations (per mirror) that SIOS DataKeeper will allow. The default value for this parameter is 4096, but a larger number may increase write performance of the mirror. The disadvantage to increasing this value is that more data will be allowed to be out of sync between the primary and secondary at any given time. See the Asynchronous Mirroring Information in Mirroring with SIOS DataKeeper for Linux for further information on LKDR_ASYNC_LIMIT
- If you are mirroring a large amount of data over a slow WAN link, it may be desirable to avoid the initial full data resynchronization and instead ship or otherwise transport a copy of the source disk or partition to the remote (disaster recovery) site. To avoid the initial resynchronization, follow the steps in Avoiding Full Resynchronizations.
- If the WAN link experiences periods of downtime in excess of 15 seconds on a regular basis, it may also be wise to tune the LifeKeeper heartbeat parameters. See Tuning the LifeKeeper Heartbeat for details.
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