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Microsoft SQL Always On Availability Group is effectively a SQL mirroring cluster. 

In a Mirroring Cluster, there is an active SQL database server and a passive database server. When the active database server is down for some reason, the cluster will fail over to the passive database server, and the passive database will become the active database server. 

In a Mirroring Cluster, only one database server is active at one time and the database operation is served from the active server only. In principle, data change in the active database is copied to the passive database in real time. 

In a Microsoft SQL Always On Availability Group, there is one single primary replica, aka, the active database, and up to 8 secondary replicas, aka, the passive databases.

Setting up a HA cluster with a Microsoft SQL Always-on Availability Group is very simple. All you have to do is to clone the primary DualShield server to the secondary server machine.

DualShield includes a utility program, dsclone that enables you to easily create a backup image of the primary DualShield server and install replica servers from the image. If the internal MySQL server was also installed when the primary DualShield was installed, then the MySQL server and database will be also included in the backup image and will be installed on the replica server machines. 

Prerequisites

  1. The replica server machine should have similar hardware and OS to the primary machine.
  2. Windows OS on both servers must have the same drive letter and the same path, e.g. c:\windows

Installation  

  1. unzip "dsclone.zip" to a folder, e.g. c:\backup where it is readable  and writable;
  2. open windows console with administrator privilege, go to the folder, e.g. c:\backup;
  3. run dsclone.exe. It will self-extract its contents to a subfolder called "clonepack";
  4. go into the subfolder, e.g. c:\backup\clonepack
  5. in the command line, run "dsclone backup";
  6. wait for it to finish;
  7. copy the entire folder, e.g. c:\backup\clonepack, to the replica machine;
  8. run "dsclone mutate" on the replica machine and follow the instructions.

Having successfully cloned the second server, you now have 2 DualShield servers installed on 2 different machines. Both DualShield servers have the same FQDN.



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