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FAQs Regarding Double-Take

SQL Server 2005

Is SQL Server 2005 supported for Double-Take®?

Advantages of Double-Take Replication

What are the advantages of Double-Take replication over native SQL Server replication?
Due to the dynamic structure of the WebEOC database and the dynamic capabilities within WebEOC to create new boards on the fly, of which create new tables and fields within the database, the standard replication capabilities built into Microsoft® SQL® do not satisfy replication requirements.

Replication Type

What is the replication type: asynchronus or synchronous?

Secondary Server Operation

In the event of failure, how does the secondary server work?
Double-Take can be configured to replicate from a primary (source) server to a secondary (target) server and failover if the source fails or stops responding. Double-Take is capable of automating the process of the target machine, standing in for the source in the event of a failure. The target, if desired, can take on the name and IP address of the failed source as well as start selected services through scripts. ESi recommends, however, that the triggering of a failover be configured to require manual intervention. Manual intervention allows an administrator to confirm the validity of the failure before proceeding with the failover process and starting SQL services on the target. Allowing a fully automated failover could result in both SQL servers being active simultaneously and, possibly, posting dissimilar data on the servers.

The Active Database in Failure

How would the application know where to look for the active database in the event of a failure?
In the event of a failure of the source machine, Double-Take can initiate a failover to the target data set. Depending on an agency’s network architecture, following a failover, WebEOC users would either log back into the system through the same web server or access WebEOC through their backup URL on an alternate web server.

Master Syncing

After a failover has occurred how does the master sync with the secondary?
Double-Take replicates SQL data continuously at the byte level from a source machine to a target machine over a shared or private IP-based LAN or WAN, ensuring that changed data is protected and can be quickly restored at all times. Once failover has occurred, if the database is activated and used on the target machine, the “master” is now on the target and remains in that state until failback.

Failback Procedure

What is the failback procedure?
Failback is an automated process through the Double-Take management console.

How long does it take to failback?
Failback timing is completely dependent upon the size of your database and the speed of the connection between the two servers.

Does failback require a outage, and is there any way to pre-sync the master to minimize failback time?
WebEOC is unavailable while the restore is in progress.

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