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Just hoping this won't be closed so i try to ask exactly as i can.

I'm in a need to buy a new server but my idea is to do many things as i can under virtualization. Because i'm a newbie in virtualization, can you point me in the right direction about which parameters should i pay attention? Are there any indicators like "Ready for Windows" stickers or etc. so i'll be sure about this or that will be fine for me?

Is it true bigger is better? Are there any indicators about 'x' Gb RAM can finely handle 'y' virtualized servers simultaneously?

Update (Some clarification on my needs):

I'd like to replace my two non-virtualized LAMP servers with one bigger server. I'm running just the usual services (LAMP, mail, DNS, FTP). The whole point is to reduce the chance of hardware-caused problems, and if it's possible (but it's out of the question here) build a fail-safe system where i'll running three virtualized system and in case of any problem one instance can take over the load from the failed one.

Please note: I'm not looking forward for any maker or exact CPU, just trying to figure out which details are important and which are not.

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closed as too localized by Janne Pikkarainen, Sven, sam, Tom O'Connor, Iain Dec 7 '11 at 22:28

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2 Answers 2

First of all you need to specify your requirements, that what exactly you want to HOST on those virtualization server(s). i can give you an Example setup and what do we need to consider in that case.

for example, Say you need to host 4 web servers , one monitoring and one AD authentication server on that virtualization server, for that you need to take into consideration these parameters.

  • RAM is the First thing, which should be as much as it can be. in your case, (depending upon 10-20 users load on server), you need to allocate atleast 2+GB of RAM to each server, which will be total to atleast 12 GB of RAM , and remember, you must always have plenty of RAM if you want the servers to run smoothly, otherwise swapping can degrade performance very badly.

  • In case of Server, you can go for any high END Xeon dual core or Quad core based server, which should have max available bus speed and at-least 2 physical CPUs(Dual core or Quad core).

  • In case of storage, the storage can be either SAS drives, SCSI drives or you can host your own NAS or SAN, to store the virtual machines. Do keep in mind, that each machine must have its own independant storage PATH for data storage, E.G, you must not share 2 servers on one hard drive. and Space of hard drives should be carefully planned. The storage must be High Speed (which you can achieve by building RAID).

i hope now you have got initial idea.

Regarding your question that how much RAM is required for number of virtualization server? it depends upon you. depending upon resources of Server, if server can have max of 24GB of RAM, then you can host 6 servers, each of 4GB RAM alocated to them. so, if you want to host more servers, you can buy new virtualization server with required RAM and so on.

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Thank you for your detailed reply. Just updated my question to clarify my requirements. Can you clarify your answer about storages? As i understood you if i have 2 HDD slots in the server i can run only one instance of virtualized system and this is without RAID. That would be scary. –  fabrik Nov 30 '11 at 12:19
    
He's generalizing; if that guest OS uses the disk subsystem intensively, it will need all the speed you can give it - which is the entire disk, in absence of RAID. –  adaptr Nov 30 '11 at 14:01

Much will depend on your choice of hypervisor.

We use vmware ESX, which offers definite advantages in some fields; other hypervisors will have their own pros and cos.

We run dual-socket quadcore boxes with 72GB each and a SAN connection for storage; we can run 20 VMs quite comfortably on that, but memory is the very first thing to run out (on Windows servers!)

VMWare only really allocates as much memory as is actively used by the guests, so you can overprovision your VMs as long as you know they won't all use their maximum amount of memory at the same time.

For some reason, this is much more visible on Linux than it is on Windows - perhaps because the Windows VMM holds on to memory longer ?

VMware also de-duplicates memory; running 10 instances of the exact same Windows version will allocate shared code only once (think OS core, libraries, etc.)

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