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Virtualization design questions for newbies

Posted on 2010-11-14
Medium Priority
Last Modified: 2012-06-21
Hello. We are considering virtualization for our production infrastructure. The idea is to create a server cluster (private cloud) that will host all Virtual Machines. I have some design questions and looking for opinions.
- Do we need redundant copies of servers if they are running on a cluster? For instance we now have two web servers on a webfarm in order to provide fault tolerance against server failures. If the VM is running on a server cluster, would you recommend to have redundant copies (ie two web servers) or would just one copy be sufficient?
- Can Windows 2008 R2 be used to create a server cluster? Do we need a special edition (ie Enterprise or Datacenter) or can Standard be used?
- If we are hosting web/application servers (not Database Servers) do we need some special storage solution?
Question by:adneprov
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Expert Comment

ID: 34133656
I would suggest using VMWare for your Virtual Server software.  They have tools to make snapshots of your existing servers so you can load them directly into a virtual server.

A Server Cluster is a good way to go for virtual servers.  You don't want 4 or more servers down because you have some kind of hardware issue.  But as far as having redundant web servers within the Virtual server may be a waste.  I guess it all depends on why you have redundant servers.  If it is for load balancing for power, then just give one server more resources.  If it is for load balancing for traffic, then make sure each redundant web server has its own Internet gateway.

You don't need a special storage solution technically.  How are you going to setup the server cluster?
It may be beneficial to have a SAN or NAS solution that can handle the throughput you require.

Check out VMware.  they have cloud infrastructure solutions as well as the Virtual Machine management..

Author Comment

ID: 34133740
hi and thanks for the prompt reply. I will look into VMWare.
Per your comments...
We currently have redundant web servers strictly for fault tolerance. Neither the traffic nor the power are so high as to require extra resources. So i suppose in this case we can have a single VM instance (?)
In regards to storage, I had read that DBs require SAN/NAS/etc. Is this because of amount of date, throughput or both? Our SQL DBs total circa 25GB.
If not using SAN/NAS/etc... is data replicated amongst the local HDs of the cluster servers? So if i have ie 5 VMs and each VM has a 10GB System Partition and a 20GB Data Partition, does it mean that each physical server in the cluster needs 5 x (10+20) = 150 GB of HD space?
LVL 42

Accepted Solution

kevinhsieh earned 1000 total points
ID: 34133763
If you use Hyper-V, make sure that you have at least 1 physical domain controller in your infrastructure.

In order to do proper clustering, you need to use run Hyper-V Server 2008 R2 (free), Windows 2008 R2 Enterprise, or Windows 2008 R2 Datacenter. I use Hyper-V Server on the hardware, and have Windows 2008 Datacenter licenses purchased to cover the Windows licenses for the virtual machines, as opposed to buying a single copy of Windows for every VM I run.

A virtualization cluster protects against hardware failure, but it does not protect against software, operating system, configuration, or other failures within the virtual machine, so it probably still makes sense to have multiple severs in your web farm. Once you virtualize, adding machines is pretty cheap.

You can use either Intel or AMD processor servers in your cluster, but you can't mix them in the same cluster.

You will need shared storage, which will probably be your biggest expense. iSCSI is generally the preferred shared storage, but you can use fibre channel as well, or shared SAS for very small scale deployments. The big name vendors are HP, NetApp, EMC, and Dell. There are lots of smaller vendors as well. Prices start at several thousand dollars and go on up from there. There are also software solutions such as Starwindsoftware.com, vm6software.com, and openfiler.com that take existing storage and make it sharable via iSCSI.

Author Comment

ID: 34134242
- why do I need a physical DC? Can't the DC(s) run as VMs?

- can i use Win2008 R2 Standard for clustering? Our physical servers already have Win2008 Std so we would like to reuse these licenses if/when we virtualize.

- can i please get more info about storage and how it is configured/used/etc? If using "local" HD space, is data from each VM replicated on all cluster servers? If using shared storage does this mean I need less HD space on the physical servers because things are stored on the shared space? Does this also apply to Virtual OS's or only to data? Can I use a NAS for storage, why does it have to be iSCSI?

much thanks!
LVL 42

Assisted Solution

kevinhsieh earned 1000 total points
ID: 34138632
Microsoft clustering requires Active Directory. If everything is shut down, including the domain controllers, how can you start your cluster if it requires a domain controller which isn't available because the cluster hasn't started yet? That's why you need to have a separate domain controller somewhere. You can virtualize the rest of them.

You can use Windows 2008 Std for Hyper-V, but not for clustering. Windows Std doesn't support clustering. You will also need Windows licenses for any VMs you have running, and you can't transfer OEM licenses from your existing servers. You can reload the physical servers with Hyper-V Server 2008, and then use your existing Windows 2008 Std license for one of your virtual machines. If you buy Windows Enterprise, that licenses 4 concurrent  Windows Server VMs on a piece of hardware. Windows Datacenter liceses unlimited copies of Windows Server to run a a piece of hardware. Otherwise, you need to buy a copy of Windows Server for every Windows server VM you run.

If you use external shared storage, then you only need as much local disk on each server as is required for Hyper-V server, which I would say is 10-15 GB + the amount of RAM you have installed.

If you want to use internal storage to the servers, there is no standard way to get the data replicated to the other nodes of the cluster. That's what 3rd party vendors like Starwind Software do. I suggest that you check them out.

The shared storage can't be NAS because Microsoft doesn't support it. VMware does, and I don't know about Xen Server. VMware allows you to use NAS for storage, but they charge for clustering and high availability. Microsoft requires iSCSI, SAS, or FC for shared storage, and they don't charge for clustering and high availability (with Hyper-V Server 2008 R2). You still need to license the Windows OS for your VMs either way.

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