What Hardware Part 4 : Simple Cluster Install

In this article we are going to talk about a simple cluster setup. If there was ever a setup that you should start with , this is the one. Whilst it may not be cheap as it uses 3 machines , it does begin to give you the redundancy that you really should have in a data collection setup.

The setup that we will talk about in this article is pictured here, this is your first step in creating a fault tolerant system.

Simple Cluster

As you can see we have just added another IIS machine to the setup. This helps us in several ways. Firstly it allows us to have more session engines , but you might ask , how does a user now get sent to the IIS machine, Which IP address should I use? The answer to this question depends on how your system has been setup. If we are talking about CATI, then the CATI room might be setup with have of the machines pointing to one ip address and the others pointing to the next. This method works , but if one machine dies , then your it will have to go around to each machine and change the IP address so we should really have a smarter way of doing this. And there is , Microsoft allows up , via software , to create 1 VIP ( Virtual IP ) that points to the two IIS IP addresses. This way we only have one IP address to use when we send out and the software , depending on how it is setup will either send all the users to one machine until it thinks it is to stressed and then send all the new users onto the second machine. The other way this can be setup is in a 50 , 50 manner where by the load is spread evenly across the two machines. We would like to add here that whilst a software load balancer is a good start , a hardware load balancer is by far the better option, but these pieces of hardware are not cheap.

Q: So we have two IIS machines and they are load balanced with a VIP, is that all we need to know?

Not really , you can have a VIP and still use the local IP as well. Take a minute to think about this situation.

I have purchased Data Collection Interviewer and Reports for Surveys Server. I only want to use Reports for Surveys Server on one machine so that it does not affect the collection of my data.

In this three machine setup we can do this , even with a VIP. If we have set the load balancer to use one machine until it is stressed we could just install the Reports for Surveys component onto the second machine and make all the reports for surveys users use the 2nd machine only and them only when things are getting a little busy would any surveys get run on the second machine.

Q: I like this setup , but what happens when one of the IIS machines fails.

This depends on what your system is running and which machine dies. We have touch on this briefly in a previous article but it is now time to re-introduce the FMROOT folder. The FMROOT folder is a share that holds all your MDD files and templates etc. It sits on one of the machines which is normally the Primary Machine. When you activate your survey , your MDD file and templates get moved to all the right places on the primary but they also get copied to the other machines in the cluster. ( not the SQL ) . So if the primary machine where to go down , then your users should be able to do things that are setup to use the local MDD files the remaining machines. So this means , that running a survey will still continue , however you will not be able to activate or setup any new jobs because the FMROOT is not available.

Q: What can I do to make my FMROOT folder safe.

The FMROOT can actually be put on a totally different server if needed and you could make sure that this server  was raided. Using a machine for just its disk space ( file server ) is more robust , as there is not allot of things running on the file server that can go wrong.

Q: Ok I am sold on this setup , How fault tolerant is this cluster Setup?

It’s not too bad , it’s not 100% , but the web tier has been taken care of , and just by adding additional IIS machines it begins to make it even more so. SQL at this stage is not really taken care of. You will see in the next article how we can take this setup, and address SQL as well as ease the load on the IIS machines.

Q: What Hardware do I Required for this Setup?

If you have decided that this setup is the way to go for you them we would recommend at least the following.

IIS Machine Primary :

  • 4 gig of memory ( 3 session engines ).
  • Quad core CPU.
  • 1 80 gig hard disk for the Operating system.
  • 1 200 gig hard disk for the data files.
  • Raid if possible.

IIS Machine Secondary :

  • 4 gig of memory ( 3 session engines ).
  • dual core CPU.
  • 1 80 gig hard disk for the Operating system.
  • 100 gig hard disk for the data files.

SQL Machine :

  • 4 gig of memory.
  • Quad core CPU.
  • 1 80 gig hard disk for the Operating system.
  • 1 200 gig hard disk for the MDF data files.
  • 1 200 gig hard disk for the LDF log files.
  • Raid if possible.

So there you have it , we have made our setup a little more tolerant, but we still have a bit to do to make a system that knows how to handle itself in a time of crisis. In our next article we will begin to expand on this setup and see what the next logical topology would be and talk about the pros and cons of it.

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