Replication: Operational considerations


Creation Date: April 7, 2009
Revision Date: February 27, 2011
Product: DS-System

Summary

The following sections describe some specific operational issues that may be encountered when using Replication. These are not exhaustive descriptions of all possibilities. They are listed to provide you with some considerations for your environment(s):

Behavior of Replication DS-System when the primary DS-System is not reachable

A DS-Client can be configured with one or more DS-System connections (For instructions see the DS-Client User Guide (dsuser.pdf) > 2 - Setup and Configuration > Change the DS-Client Configuration > Edit the Settings for DS-System Access).

Each primary and secondary DS-System connection can have one or multiple IP addresses. When DS-Client tries to connect to a DS-System, it will try to connect to each IP address specified in its "Primary" Connection. DS-Client only considers secondary addresses after trying all the IP addresses listed in the "Primary" Connection.

If DS-Client connects to a secondary DS-System, it can always perform restores, however its ability to back up new data depends on the type of license running on the secondary DS-System:

Multi-Directional Replication will replicate DS-Client database dump files

This feature is managed from the DS-Operator > Setup Menu > Advanced Configurations: "ClientDBDumpDays" parameter.

Any backed up dsclient database dump files are replicated from one DS-System to another in the Replication Group based on whichever DS-System has the latest dump. If a DS-Client must be recovered (e.g. from a total hardware failure) and it connects to a Replication DS-System (where it has never run a Daily / Weekly Admin activity), that DS-Client will still be able to recover the databases (provided the dumps have been replicated).

On each DS-System, the "ClientDBDumpDays" parameter is configured separately, to determine how many days' worth of dumps to keep. Note the size implications of increasing this parameter, since it applies to all the DS-Clients on the DS-System.

Considerations about Multi-Directional Replication speed

In a basic Replication Group configuration, both the primary DS-System and secondary DS-System may reside on the same subnet / LAN. As a result, the Replication process will always be up-to-date on the secondary DS-System, since the Replication process speed between the DS-Systems is faster than the backup speed to the production DS-System (i.e. LAN speed vs. WAN speed).

In a configuration where the DS-Systems are replicating over the WAN, the replication speed may not be as fast as the backup to the primary DS-System. In these situations, the Replication DS-System may not always be up-to-date.

Synchronization process for DS-Clients connecting to different DS-Systems in the same Replication Group

This applies to:

When DS-Client backup sets are marked as "out-of-sync", DS-Client will try to connect to all DS-Systems by using the IP addresses in its "DS-Client Configuration Connections Tab" screen. DS-Client will determine the most up-to-date DS-System, and will synchronize its data with that one.

Time between backup windows to allow replication to complete

The DS-System replication is asynchronous and a replication will only be done after backups have completed. Backup and replication will not run concurrently.

Which DS-System is the 'source' and which is the 'destination'

When replicating data, the DS-System Group will pick one of the DS-Systems as a "source" and another as the "destination". This is done based on the last connection time of the DS-Client:

Automatic fail-over (of DS-Clients to alternate DS-System) - critical notes

Multi-directional replication has the following impact on automatic fail-over:

See Also



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