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Windows 2008 R2 host clustering versus VM clustering
I have been reading up on host clustering versus VM clustering with Windows 2008 R2. Let's assume I have two VM's for which I want to have hardware redundancy. It seems I have two choices: I can cluster two physical servers hosting the two VMs at the host level or I can have two physical servers and can cluster at the VM level.
I have a couple of questions:
I understand I need 2008 R2 Enterprise or better or HyperV server to be able to do host clustering - I can't use 2008 R2 standard. What about VM clustering? Can I use 2008 R2 standard?
Regardless of the above, why would I ever choose to cluster the VM's individually as opposed to simply clustering the host? Wouldn't I need a separate shared cluster disk for each VM as opposed to a single shared cluster disk with host clustering?
I have a couple of questions:
I understand I need 2008 R2 Enterprise or better or HyperV server to be able to do host clustering - I can't use 2008 R2 standard. What about VM clustering? Can I use 2008 R2 standard?
Regardless of the above, why would I ever choose to cluster the VM's individually as opposed to simply clustering the host? Wouldn't I need a separate shared cluster disk for each VM as opposed to a single shared cluster disk with host clustering?
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I'd recommend to do cluster between two physical servers and install Hyper V in CSV (Clustered shared volume) with 2008 R2 Enterprise. You can leverage the benefit of running two VMs in two hosts for different applications in redundancy.
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kevinhsieh:
Thanks for the quick response.
If I understand you correctly, when I have two servers that are running a clustered File Server at the host level and physical server A crashes I will failover to server B; however if the situation is that the File Server VM fails - not hardware, some OS issue - then nothing will happen with host clustering only VM clustering would deal with that situation by failing over to the clustered VM node - the host wouldn't notice anything wrong at all - it only notices when its OS is corrupted or if the server hardware fails?
I can definitely see the value of clustering/DAG for Exchange.
What about VM clustering for the following specific situations:
File server?
A server that is running a single critical app that is SQL-server based?
A server that is running a single critical app that is not SQL-server based?
A Web server?
A Terminal Server/Remote Desktop Server?
Finally let's say I have two different kinds of VM's that I am hosting on a server and I want to cluster them at the VM level, will I need two separate shared clustered volumes for each VM?
Thanks for the quick response.
If I understand you correctly, when I have two servers that are running a clustered File Server at the host level and physical server A crashes I will failover to server B; however if the situation is that the File Server VM fails - not hardware, some OS issue - then nothing will happen with host clustering only VM clustering would deal with that situation by failing over to the clustered VM node - the host wouldn't notice anything wrong at all - it only notices when its OS is corrupted or if the server hardware fails?
I can definitely see the value of clustering/DAG for Exchange.
What about VM clustering for the following specific situations:
File server?
A server that is running a single critical app that is SQL-server based?
A server that is running a single critical app that is not SQL-server based?
A Web server?
A Terminal Server/Remote Desktop Server?
Finally let's say I have two different kinds of VM's that I am hosting on a server and I want to cluster them at the VM level, will I need two separate shared clustered volumes for each VM?
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kevinhsieh::
Thanks for the additional detail. It gets my brain chugging. You write:
You are correct in that if you have host level clustering only and a file server VM fails, (the Server service crashes, or even a blue screen) the hypervisor won't know that there is a problem and you will need manual intervention. The hypervisor cluster knows when the host nodes have gone down or are otherwise unavailable due to networking issues and will take action. They can even know when the VM has crashes and lost its heartbeat (I don't yet know how you actually DO anything about that in Hyper-V). I believe that System Center Operations Manager can look deep into the server (physical or virtual) and take action if something is amiss.
By Hypervisor cluster above you mean the VM cluster?
Also you make references above to crashes in the VM and the HyperVisor knowing. And earlier you state that the host cluster can't deal with:
OS failure, application failure, database corruption
I am unclear how it would be that in any of the above circumstances why the fail-over wouldn't fail over to a VM that has the same problems - aren't the VM's in synch?
As far as types of servers that VM clustering can be used for, what about an AD server? I didn't list that. I know it might not be best/official practice but would it work at all?
You write:
"For failover clustering using VMs, each cluster will need its own dedicated access to cluster storage LUNs."
What do you mean by dedicated access? Perhaps a 'picture' might help. Let us say I have two physical servers and I have two VM's that I want to failover cluster? What will the storage look likein this situation? How many drives? How many ISCSI targets?
Thanks for the additional detail. It gets my brain chugging. You write:
You are correct in that if you have host level clustering only and a file server VM fails, (the Server service crashes, or even a blue screen) the hypervisor won't know that there is a problem and you will need manual intervention. The hypervisor cluster knows when the host nodes have gone down or are otherwise unavailable due to networking issues and will take action. They can even know when the VM has crashes and lost its heartbeat (I don't yet know how you actually DO anything about that in Hyper-V). I believe that System Center Operations Manager can look deep into the server (physical or virtual) and take action if something is amiss.
By Hypervisor cluster above you mean the VM cluster?
Also you make references above to crashes in the VM and the HyperVisor knowing. And earlier you state that the host cluster can't deal with:
OS failure, application failure, database corruption
I am unclear how it would be that in any of the above circumstances why the fail-over wouldn't fail over to a VM that has the same problems - aren't the VM's in synch?
As far as types of servers that VM clustering can be used for, what about an AD server? I didn't list that. I know it might not be best/official practice but would it work at all?
You write:
"For failover clustering using VMs, each cluster will need its own dedicated access to cluster storage LUNs."
What do you mean by dedicated access? Perhaps a 'picture' might help. Let us say I have two physical servers and I have two VM's that I want to failover cluster? What will the storage look likein this situation? How many drives? How many ISCSI targets?
Are we talking VMWare or HYPERV clusters? With a VMWare cluster and HA if a VMWare host fails the virtual machines will be restarted. If you are using Fault Tolerence then the two machines run in-step on separate hosts, but note Fault Tolerence only supports on CPU (i.e. core) per server.
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Sorry but I'm not understanding. I need something more specific. Per my question I need a detailed example:
"Let us say I have two physical servers and I have two VM's - File Server, Terminal Server - that I want to failover cluster? What will the storage look like in this situation? How many drives? How many ISCSI targets?"
So the File Server cluster requires a quorum LUN, let's call it LUN 1? Is this a dedicated ISCSI drive? Or just a partition on a dedicated ISCSI drive?
And the File Server cluster requires a separate quorum LUN, let's call it LUN 2? Is this a dedicated ISCSI drive? Or just a partition on a dedicated ISCSI drive? Can an ISCSI drive host two quorum disks? Or each quorum disk has to be a separate physical drive?
As far as data for the cluster, do I need separate physical drives for the data for the File Server cluster and the data for the Terminal Server cluster? Or can I share a physical ISCSI drive with one partition for the File Server data and the other for the Terminal Server?
At the extremes could I just create one huge ISCSI drive with partition 1 for File Server quorum disk, partition 2 for for Terminal Server quorum disk, partition 3 for File Server data and partition 4 for Terminal Server data or do I need four separate physical drives to accomplish this?
"Let us say I have two physical servers and I have two VM's - File Server, Terminal Server - that I want to failover cluster? What will the storage look like in this situation? How many drives? How many ISCSI targets?"
So the File Server cluster requires a quorum LUN, let's call it LUN 1? Is this a dedicated ISCSI drive? Or just a partition on a dedicated ISCSI drive?
And the File Server cluster requires a separate quorum LUN, let's call it LUN 2? Is this a dedicated ISCSI drive? Or just a partition on a dedicated ISCSI drive? Can an ISCSI drive host two quorum disks? Or each quorum disk has to be a separate physical drive?
As far as data for the cluster, do I need separate physical drives for the data for the File Server cluster and the data for the Terminal Server cluster? Or can I share a physical ISCSI drive with one partition for the File Server data and the other for the Terminal Server?
At the extremes could I just create one huge ISCSI drive with partition 1 for File Server quorum disk, partition 2 for for Terminal Server quorum disk, partition 3 for File Server data and partition 4 for Terminal Server data or do I need four separate physical drives to accomplish this?
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Thanks for the explanation - I am getting the picture.
You write:
"Each cluster needs its own set of LUNs."
So if I had two File Servers for some reason, each one would require two LUN's - one for the quorum and one for the data, a total of 4 LUN's that could reside on one physical ISCSI drive?
I don't have ISCSI setup yet - just looking at it. Do you have any recommendations?
You write:
"Each cluster needs its own set of LUNs."
So if I had two File Servers for some reason, each one would require two LUN's - one for the quorum and one for the data, a total of 4 LUN's that could reside on one physical ISCSI drive?
I don't have ISCSI setup yet - just looking at it. Do you have any recommendations?
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Thanks for the further info. What I was referring to was two different file servers I want clustered. For the sake of argument file server 1 has files that go from A-L and file server 2 has files that go from M-Z. So there are two clusters - File Server A-L and File Server M-Z. So in that case I need 4 LUN's on one physical ISCSI target?
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Thanks for your patient explanations.
The second option is clear but as far as the first option let me explain back to see if I have the correct idea. I think you are saying that I would separate out files from system e.g. operating system files let's call it C so in effect I have one file server C drive that contains only OS with an A-L data drive attached to it and an M-Z data drive attached to it. I would then need one ISCSI physical device partitioned as follows:
one LUN for the system C drive
one LUN for the A-L data drive
one LUN for the M-Z data drive
one quorum LUN to allow clustering of the entire file server - C, A-L and M-Z - with another physical server
In this situation, if I understand it correctly, the entire file server is 'failed over' if there is a problem as opposed to option 2 where only one File Server would be failed over - the one that is having the problem?
If that's the case it's identical to host clustering in the situation where the file server VM's are the only VM's on the physical computer - yes?
The second option is clear but as far as the first option let me explain back to see if I have the correct idea. I think you are saying that I would separate out files from system e.g. operating system files let's call it C so in effect I have one file server C drive that contains only OS with an A-L data drive attached to it and an M-Z data drive attached to it. I would then need one ISCSI physical device partitioned as follows:
one LUN for the system C drive
one LUN for the A-L data drive
one LUN for the M-Z data drive
one quorum LUN to allow clustering of the entire file server - C, A-L and M-Z - with another physical server
In this situation, if I understand it correctly, the entire file server is 'failed over' if there is a problem as opposed to option 2 where only one File Server would be failed over - the one that is having the problem?
If that's the case it's identical to host clustering in the situation where the file server VM's are the only VM's on the physical computer - yes?
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I will read through several times and get back to you if I have any further questions.
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Thanks for giving me the time to absorb this. I think I understand the basic strategy.
At the end you write: "Now, let's suppose that VM1 is active for the file share data and it is running on HOSTA, which crashes. Two failovers will then happen. First, VM2 will start serving the files, just like in the first case. Secondly, VM1 will get rebooted on HOSTB, because that is what happens to VMs when you cluster the hosts."
What I think you are saying is that with HOST A crashed, Host B is now running clustered VM's as in the single host situation with VM2 being the active VM and VM1 being the failover one. So in this case if for some reason VM2 bluescreened, VM1 would take over.
At the end you write: "Now, let's suppose that VM1 is active for the file share data and it is running on HOSTA, which crashes. Two failovers will then happen. First, VM2 will start serving the files, just like in the first case. Secondly, VM1 will get rebooted on HOSTB, because that is what happens to VMs when you cluster the hosts."
What I think you are saying is that with HOST A crashed, Host B is now running clustered VM's as in the single host situation with VM2 being the active VM and VM1 being the failover one. So in this case if for some reason VM2 bluescreened, VM1 would take over.
Yes, I think that is correct.
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Great. Thanks for all the help.
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Excellent responses.