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virtualization: Xen (unraid)


IrishFavor
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So i have searched a bit on the subject and have yet to find a definitive answer, maybe its my lack of google fu or just laziness. Anyway I am starting to get into virtualization specifically a hypervisor. I think I am going the route of Xen as I already have a NAS running UnRAID 5. So I came to the logical conclusion I should just upgrade to UnRAID 6 because it has an option for Xen.

Question:

When using a hypervisor and setting up a server cluster do the CPU of each server have to match? Or is this only needed if you plan on moving the VM's from one server to another?

Thank you in advance for any Information. Also can anyone recommend a good firewall? As I am running an AP\ Firewall (ASUS), and would like to upgrade to something more substantial. I remember there were a few segments about smoothwall, monowall, ect. just wanted to see what the community uses.

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Only thing I can comment on is the CPUs: You can go absolutely bonkers with this. It's possible to have 4 cores in your system, and on that run 4 VMs with 4 CPUs each. The only thing I think you're not allowed to do (made impossible because it doesn't make sense) is to assign more CPUs to a machine than the host physically has.

There's no harm in over-provisioning so long as all VMs don't get loaded to the max at the same time as would impact performance considerably.

How many cores to each of your whatever many VMs is something you need to discover as it's fully dependant on the load your VMs end up placing on your system, and what level of performance you still find acceptable. It does help quite a bit to have sufficient actual RAM in the system for all your VMs. In the case of XEN you can once again over-provision a bit as it will only claim from the host the amount of memory that's actually used, but best is to just assign a fixed amount to each VM and have at least as much memory in the system as the VMs combined think they have and preferably a little bit more for the host itself.

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Thanks for the info, it helps allot. I just wasn't sure when it came to the CPU and leveraging other machines resources. Please correct me if im wrong but it sounds like what you are saying is that if i have 2 servers with lets say 2 quad core CPU's and 32 GB of ram. I should then be able to run, to make it easy as possible 8 VM's with 8 cores and 4GB of ram on each server? However we are not sure if i would be able to leverage the resources from the second server to for example make a 16 core 64 GB VM?

Maybe if i explain further this will make more sense, I have 2 servers 1 is a Quad Core Xenon with 8GB of ram and 20TB of HDD. The other is a Dual core Xenon with 16GB of ram and 3TB of HDD. These Servers have different generation CPU's, what im looking to do is to setup a cluster so that i can allocate the Resources from both servers. I would like to be able to Run an AD\ Exchange server, Asterisk, UnRaid, Home automation servers then perhaps a few Windows based VM's.

Now i am not opposed to getting another server if need be but i would like to leverage the hardware that i have, Most Importantly is the 20TB for the Media. So if i cant combine the resources would i have to run it as a different type of appliance such as a SAN?

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Yeah, clustering is out. I've been told that with VMWare you can migrate an instance to a different node, the instance barely skipping a beat as it goes, but that's highly specific stuff probably not yet available on Xen. The best I would expect from there is that I can stop/hibernate the instance on machine 1 and then start it again on machine 2 if they both have access to the same bit of storage.

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OK that make a lot of sense, I have been doing some research on Resource pools http://knowcitrixx.wordpress.com/xenserver-6/resource-pool/. It sounds like what your saying is I can create a resource pool, but the vm can only use the max resources of one server and if need be moved from one server to another. As long as its not using resources from both at the same time.

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Yeah, clustering is out. I've been told that with VMWare you can migrate an instance to a different node, the instance barely skipping a beat as it goes, but that's highly specific stuff probably not yet available on Xen. The best I would expect from there is that I can stop/hibernate the instance on machine 1 and then start it again on machine 2 if they both have access to the same bit of storage.

It's also stupidly expensive.

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It's also stupidly expensive.

Well, if your hosting client is willing to pay through the nose for next-to-no downtime, the product swiftly pays for itself.

In all other cases (which tends to be the majority of cases) you're absolutely right of course.

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Well, if your hosting client is willing to pay through the nose for next-to-no downtime, the product swiftly pays for itself.

In all other cases (which tends to be the majority of cases) you're absolutely right of course.

I've got a hospital client that uses it. They run all their electronic medical record nurse's stations off a vmware thin client system. All the clients are hp thin client machines that look like all in one computers, but they don't have much of the computer part. It's a pretty slick system. All of it is run from I think 4 cisco vm servers with several hundred terabytes of san for the data.

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Yea that's my goal, unfortunately i have to wait for more funds. so that i can buy a bigger server rack for the house. As i have one server with the 24 HDD bays is there a way of turning that into a SAN so that when i create a resource pool for the HDD's i can add that machine? i assume that once i set it up as a SAN i would not be able to use the CPU resources in a Pool?

If that is not an option can anyone recommend an inexpensive SAN?

Edited by IrishFavor
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