In the age of catastrophes, which include disk failures,
power failures, fires and floods, disasters can take their toll on any business
and stop the flow of information. With each minute of lost data translating
into unrecoverable revenues, downtime is being taken seriously.
As a DBA today in the IT field, we are in an age of zero
downtime if possible. To make this dream come true, NSI’s Double-Take software
provides high availability for Windows 2000/2003 machines running SQL Server
2000. The software allows a secondary SQL Server to take over the identity of
the failed SQL Server while suffering no disruption or data loss. In this
article we will discuss how to install and configure Double-Take for
replication and mirroring.
How does it Work?
Double-Take software gives you the ability to configure a
Source and Target machine and choose the directories and folders that you want
to replicate from Source to Target. Double-Take uses a delta-replication strategy which only sends the changes since
the prior replica. This provides a real-time fast replication of data from one
server to the other minimizing the bandwidth. This is a very popular model for
pushing data over a WAN.
In order to successfully show you how to implement this
strategy, you will need the following:
- 2 Windows 2000/2003 servers
- 2 copies of SQL Server 2000
- 2 copies of Double-Take 4.x
I created my lab using VMWARE
Workstation; this is a great piece of software for running multiple
environments on one machine or server. First, I configured basic Windows 2003
Server installations followed by the installation of SQL Server 2000 (w/ SP3A)
and finally Double-Take. You can install Double-Take by just accepting the
Configuring Double-Take on the Source Server
The only initial configuration on the Source server is to
install the Operating System (OS), SQL Server 2000 with Service Pack 3A and
finally load Double-Take.
Configuring Double-Take on the Target Server
After the installation of Double-Take is complete, click
Start | Administrative Tools, Services and choose the Double-Take service as
shown in Figure A. Next, click the Log On folder and select Allow service to
interact with desktop.
Click OK and shut down the following services on your target
- Message Queuing (If installed)
- Distributed Transaction Coordinator (DTC)
Once you have shut down these services, you will also need
to set them to a manual status. Now that we have configured both the Source and
Target, let’s move on to configuring Replication and Mirroring.
Configuring Replication and Mirroring
Let’s begin by clicking Start | Double-Take | Management
console as shown in Figure B. Next, Double-Click your Source machine to logon
(Figure C). In this lab, Belle is the Source server. Our next step is to
right-click on the Source machine and choose Properties. Then, choose
the Setup tab and deselect Perform Remirror After Auto-Reconnect (Figure
D). If you do not deselect this, the source server could overwrite the target
after a failback.