CLUSTER REPLICA

Cluster och replikering för MS-SQL. Kräver inga MS server enterprise versioner. Endast Windows2003/2000/xp  servrar. Inga ytterligare krav eller ändringar på hårdvaran

Realtids filreplikering i klustrade windows servrar. Öppna och låsta data filer replikeras. Vid system stop eller krasher tar över klustrade server. Kritiska applikationer, IIS WEB servrar, oregelbundna system verblastningar kan ha nytta av klustring och SQL server filreplikering.

ClusterReplica is a cluster software that handles data replication. All types of files, including MS SQL files, can be replicated in real time, and even the file is open or locked. Running on two identical Microsoft Windows systems, ClusterReplica binds the systems into one cluster server of an ACTIVE station and a STANDBY station. The failover and failback features of ClusterReplica ensures data availability.

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Let's take a look at the first situation:
The data structure is on the same system as the network server

ClusterReplica will be installed on the network server systems.

Because ClusterReplica also includes the failover/failback features, the network server can use it for server availability functions. To use ClusterReplica, you need to set up two identical servers and, with ClusterReplica running on both systems, you configure one as the active server, the other the Standby server.

Your new network server can be seen as the systems in the brown box of following picture. Here the two systems function together as the network server now : to network clients, the server IP will always be the one of the active server system. Data replication is only from the ACTIVE server to the STANDBY server when both systems are functioning normally.

• Above picture shows how the cluster server works when both ACTIVE and STANDBY servers are running normally.
  
  
• The next picture shows the situation when the ACTIVE server is down.
  

  Your network server is now in Failover state:    Now, the Standby server is activated and all of network service requests and newly entered data are going to the STANDBY system. To the network clients, however, their network access IP remains that of the ACTIVE servers - nothing is changed.

• After five hours of hard work, you fixed the problem on the ACTIVE server, and reconnected it to the STANDBY server.
  

  Before activating the ACTIVE server, you are facing the choice of:

  • replacing the data on the ACTIVE server with the updated data now on the STANDBY server
  • or not replacing the data

  With this question settled, the network server will be back running normally again.

Your new database server now includes an active server and a standby server. The systems included in the brown box is functioning together as your new database server now : Notice that the data replication is only from the ACTIVE server to the STANDBY server when both systems are functioning normally.

1. Above picture shows how the cluster server works when both ACTIVE and STANDBY servers are running normally.
   
   
2. The next picture shows the situation when the ACTIVE server is down.
   

   Your network server is now in Failover state:    Notice now all new data coming from the network server will be stored directly on the STANDBY server.

• After five hours of hard work, you fixed the problem on the ACTIVE server, and reconnected it to the STANDBY server.
  

  Before activating the ACTIVE server, you are facing the choice of:

  • replacing the data on the ACTIVE server with the updated data now on the STANDBY server
  • or not replacing the data

  With this question settled, the network server will be back running normally again.

Failover is the process specifically associated to cluster systems. Typically it means when the Primary station of a cluster system dies, the Secondary station will be activated to take over the active duty of the Primary station. This feature supports the high availability of the cluster server.

XLink's ClusterReplica Standard edition binds two Windows systems together as the cluster server, which is best applicable for web server and file servers. It will monitor the systems in the cluster system and the pre-defined services to determine if the cluster system is in the condition that a failover should be activated.

Failover conditions

ClusterReplica makes decisions on activation of failover on three types of conditions:

1. System failover - This happens when the entire Primary system is down
2. Service level failover - When any one of the monitored services is not functioning normally

Detailed explanations of these conditions are listed below.

1. System Level Failover

   The first picture (1) below shows a normal working situation of the cluster server. When the Primary station fails, the Secondary Station will become the Primary station and work in STAND ALONE mode as seen in picture (2).

2. Service Level Failover

   Failover will take place when one of the services fails to function normally. In this situation, both clustered systems will be running. However, their roles of ACTIVE and STANDBY will be switched automatically. 

   NOTE: when the ACTIVE station is changed to become the STANDBY Station, you know there is a service or application on that system failed to function normally. You should exam the Secondary station and fix the problem without delay. Resetting the cluster system is also important.

Here are some pictures to provide a general description of Failover (1)(2) and Failback (3)(4).

The Registry Replication functionality meets the needs of some server systems which require certain dynamically changed key definitions of registry matched on the Secondary server for a successful failover.

When to use "Registry Replication"

Use Registry Replication only when it is absolutely necessary. Because the registry controls the operation of the entire system, it is recommended that you don't change any thing in it unless you know precisely what you are doing.

Warning: Do not replicate the entire registry - replicate only the keys that are needed.

• When to use Failover Shared Folder

  Failover Share Folder is designed for network drive sharing on the cluster server.

  If you have drives or folders shared out for network usage (through Windows "map network drive"), you will need to setup this configuration to ensure the drives or folders to be properly shared out on the Secondary server when the Failover occurs.

• Typical applications of Failover Shared Folder

  Web server and File server are the typical examples in need of shared folders.  IT personnel may need to access the web site remotely for web page updating. Network clients of a file server may nee to get a shared folder for local use for high convenience and efficiency.

  For these reasons, shared folders failover can guarantee non-interruption of works and no loss of data.