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How many virtual machines can this server support?

Posted on 2010-08-19
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Last Modified: 2012-05-10
How many virtual machines do you guys think this server can support?

Virtual machine: Windows 2008 64bit, Exchange 2007 Standard, 50 mailboxes, 1GB each, 1000 emails a day, 250GB HD with ThinProvisioning

Vmware ESX 4.0

Hardware:
Dell PowerEdge R900, Dual 6 core, L7455 Xeon 2.67Ghz, 16M cache, 1066 Mhz,
Memory 128GB
2x 15k RPM internal drives, SAS 6.0Gbs RAID card
Dell PowerVault MD1220 (JBOD), 12x 2TB 7.2K RPM NearLine SAS 6Gbps hard drives in RAID 10


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Question by:PaperTiger
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by:coolsport00
ID: 33480827
It's difficult to give you an exact number "PaperTiger", but the number would be somewhat high, given you have two 6-core CPUs and 128GB RAM. You are really only limited by the physical resources. So, whatever sys req's you need for a phys server, also applies to a VM. You just have to compensate a small additional resources to the hypervisor (1GB RAM minimum, small amt of CPU, and 10GB disk space). After that, whatever you can put on it, do so :)  I know that's a vague answer, but there is no exact science to it other than being limited by your hardware resources.

Regards,
~coolsport00
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by:Luciano Patrão
ID: 33480836
Hi

I don't understand the 1st server(the Windows). Is this the example of VMs that you will use?

Regarding the ESX host, with that type of server, and that amount of memory, I think you can easily put 30 VM

Of course this all depends of the type of VM that you will use. If is file server, mail server, web server, app server or database server. But i think the average will be this

You don't informe in your question, but is important to ask the number of nics. At least 10 nics for that server

If your 1st server is a example, then we need to reduce to maximum of 20 servers. Again the nics are very important on this design

Hope this ca help

Jail
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by:coolsport00
ID: 33480843
We can do a 'hypothetical' though. So, for example, say you have VMs that require 30GB HD space, 1 vCPU, and 2GB RAM. If you subtract 4GB RAM off the bat that the ESX host needs, and 10GB of space, you can then 'divvy' up the rest of your resources to come up with how many VMs you can have. As far as CPU goes, it's not a 1 to 1 allocation (i.e 1 vCPU per 1 Core). ESX/i disperses and, if needed, overcommit CPU resources because not all CPU is need all the time by every VM. So, just with the resource example I gave you above, you could have at least 40 VMs, and that's only limited by your RAM, because you have enough disk space (it's 2TB, correct?).

~coolsport00
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by:Luciano Patrão
ID: 33480863
Hi

@coolsport00

That is what i sum every time i need to check the server. After i will reduce for safe i will reduce the number

So yes, depending always the type of server, the number will be between 30 to 40. And if yes small servers you can put 50. Mas this is just only in special cases

Jail
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by:PaperTiger
ID: 33481015
Sorry, I thought I specified what kind of virtual server. It is the one listed in my question - W2K+Exchange etc. I want to know how many of that I can support with my hardware.
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by:Luciano Patrão
ID: 33481051
Hi

You will have all servers like this? If so, will consume lots of memory and CPU

With the 2Tb Storage you only can allocate 8 VMs

I think this will consume about 6Gb(minimum) memory for each server, but if we put 8Gb for each you can get 16 VMs

So regarding the Storage you can only allocate 8 VMs, so i think this is the maximum that you can allocate on this host

Jail
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by:PaperTiger
ID: 33481090
This is just a theoretical question.

Storage is not a limit because it has 6TB. I would agree the memory is a limiting factor. So 16-20 would be my guess.
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by:coolsport00
ID: 33481102
Oh...ok, so 1 VM will have all that running on it; yes!...certainly a RAM hog. You would have a min of 6GB RAM and, given the user-base (only 50), that should be plenty, although I wonder about their mailbox size...are they using email as file storage!?!?! (if you can't tell, that is one of my utmost PET PEEVES!) :P haha

Yeah, you won't get more than 20 of those kind of VMs on your host then.

Regards,
~coolsport00
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by:Luciano Patrão
ID: 33481104
Hi

Sorry i see 2Tb but i did not notice the x

So you will have 12 x 2TB = 24Tb Storage?

But if Storage is not an issue, then yes you can have between 16/20VMs

Like i said before, the network is very important also. For some type of server you need teaming, and also create some teaming for the ESX Host.

Jail
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by:PaperTiger
ID: 33481162
So the CPU is not the limiting factor?
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by:coolsport00
ID: 33481177
No, not really...RAM will limit you 1st, but yes, at some point you would need more CPU.

~coolsport00
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by:PaperTiger
ID: 33481189

Coolsport, can you define "some point" please? How should I gauge that?

If I go to 192GB memory, I can have another 10 more easily?
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coolsport00 earned 200 total points
ID: 33481303
Ha..well, that's getting back to my orig answer. There is no tool (again, that I'm aware of) that determines how many VMs can run on a host given the CPU. ESX allocates CPU resources based off a VMs request for CPU. But, lets take a different aspect to your query - suppose we did allocate explicitly 1 vCPU per VM. With hyperthreading enabled (a technology that doubles CPUs), you could theoretically have 24 VMs. But, this may not be doable because there will be times when a VM requires more CPU due to increased usage. Because CPU usage on a high I/O VM is not consistent, you can't accurately predict what you're wanting to know...only guess. A good read I recommend is the Res Mgt Guide from VMware's site. That should help clarify a little.

~coolsport00
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by:PaperTiger
ID: 33481322
Can I assume the 20 guesstimate is based on 2x6core CPUs this machine has?
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by:coolsport00
ID: 33481336
Yes...6 cores x 2 + hyperthreading enabled minus overhead needed by the host.
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Assisted Solution

by:bgoering
bgoering earned 150 total points
ID: 33481608
In my experience RAM has always been the limiting factor for number of VMs you can run. I run more of a mixture of vms, web servers, mail servers, domain controllers, WSUS, various appliances, etc. and can get 70 virtual servers on a single IBM 3950 M2 4x4 Core (16 cores) 128 GB RAM, SAN Storage and the server isn't breathing too hard.

I don't run any quite like you specified but maybe this will help.

Good Luck
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by:PaperTiger
ID: 33481882
bgoering, I assume your SAN is using FC, right?
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by:PaperTiger
ID: 33481894
Jail, why NIC would be an issue with 20 servers? Since most Internet is less than 100Mbps, I think 2 gbps NICs should be good enough, no?
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by:Luciano Patrão
ID: 33482591
Hi

2 Nics?? For 2 nics you will share your Service Console with your Network nics, and of course this is not recommended. Or if you isolate your Service Control, you will have only on nic for Network

A good ESX host, have all network, service console, vmkernel, etc., isolate and never share a nic

Jail
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by:Luciano Patrão
ID: 33482645
Hi

Not service control, but service console

Sorry

And if will have all this server with mail etc., you need to think about that you could have a link down, so you need to have teaming with more than a nic

Since almost of my costumer servers are very important and cannot afford to have just 1m down, all this design must be configured and implemented

Jail
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by:PaperTiger
ID: 33484354
From speed point of view it is OK with just 2 NIC but not from High Availability point of view?
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by:coolsport00
ID: 33484406
Yes; I run vMotion, SC, and general ntwk traffic from 2 NICs and it works just fine. It would be beneficial to have more NICs, but you should be ok. I have yet to see where NIC traffic is a bottleneck. Not saying that sometimes it isn't, it's just I have yet to see it.

~coolsport00
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by:bgoering
ID: 33484504
Yes PaperTiger - I am running a FC SAN.
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by:Luciano Patrão
Luciano Patrão earned 150 total points
ID: 33484559
Hi

High Availability point of view yes is very important. But it depends on on the infrastructure, or the type of the infrastructure, and also the client

Some clients want the design of that infrastructure, very well structure(and I must agree) when business is the 1st important think

Just finish a Datacenter migration(from P2V) and the new ESX host(about 30) are all with 10nics each and all the connections are separated

And have the minimum 2 ports for each service, this High Availability

Because inside of each host, is VMs from many different clients, and some VMware Clusters have more then 50 different vlans

Jail
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