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T O P I C    R E V I E W
JamesNT Posted - 11/01/2011 : 11:17:49 AM
I have a server with two E5504 quad core procs. These procs are NOT hyper-threaded. The problem is that with two virtual machines and the host I am out of virtual processors.

2 for the host
4 for the 2003 terminal server
2 for the sql server
= 8 vProcs which accounts for all 8 cores (4 cores per proc).

In order to get more out of this machine, I thought about upgrading to E5520's (these are also quad cores) which are hyper-threaded. This way, I would have more virtual procs and, therefore, can put more virtual machines on this server.

Question: Will this affect performance of the Terminal Server or are 4 vProcs from a non-hyperthreaded proc the same as 4vProcs from a hyperthreaded proc?

JamesNT
15   L A T E S T    R E P L I E S    (Newest First)
wobble_wobble Posted - 11/01/2011 : 3:51:31 PM
James,

maybe I'm missing something, but what % of CPU usage are you at?
Why do you think over-commiting CPU will result in latency for the users.
If you talking about having 90 TS users on a virtual guest, isn't that supposed to be the require an extra 30% resources, or did that change?
Also, as I understand it, HyperV does not allow us to specify a Core for the processing on a guest, so technically, your guests could all be running on a single core, and therefore your Host, SQL and TS could all be using the same core...or did that change?

The reason I suspect your seeing a boost on performance is because of the sharing of the cores. But unless your at 80% CPU, I'd add guests or suggest moving to a different Hypervisor as opposed to spending 1000 dollars.

My 2cent.
JamesNT Posted - 11/01/2011 : 2:56:15 PM
I think I'm just about ready to settle on the idea of setting up a second 2003 TS and getting those hyper-threaded quad core procs. I can get two E5520's for just under $1000.00 from Dell brand-new.

JamesNT
wkasdo Posted - 11/01/2011 : 2:28:53 PM
> Wasn't the argument only about scaling from 1vCPU to 2 (or 4) - because of the HAL change?

Nope. I saw testdata for Windows 2003 that showed that scaling was definitely non-lineair going from 2 to 4 vCPU. In most cases 4 vCPU was indeed faster (not all), but two VM's with each 2 vCPU beat the VM with 4 vCPU.

From that sort of result, it was decided to take the 4 vCPU variant out of the test matrix. So yes, it wil probably work just fine AND be faster than 2 vCPU (but not twice as fast!), but it's unsupported.
JamesNT Posted - 11/01/2011 : 1:42:39 PM
It appears the "gut test" is going to win out on this one.

JamesNT
Rambler Posted - 11/01/2011 : 1:38:07 PM
quote:
Not only is 4 vCPU on 2003 unsupported, performance with 2 vCPU's might actually be better than a 4-vCPU 2003 VM.
Possibly on H-V, but we were running 4 vCPUs 2k3 terminal servers on ESXi and they definitely performed better than when having only 2 vCPUs :) Wasn't the argument only about scaling from 1vCPU to 2 (or 4) - because of the HAL change?
JamesNT Posted - 11/01/2011 : 1:28:17 PM
wkasdo,

It appears I need a second terminal server, then. Reducing the vCPU's to two for the one I have now will reintroduce lag.

JamesNT
wkasdo Posted - 11/01/2011 : 1:16:24 PM
> Where is it documented that 2003 with 4 vCPU's is unsupported?

It says so here: http://technet.microsoft.com/en-us/library/cc794868(WS.10).aspx

Actually, Mark's book on 2008R2 says the same thing.

> The guys at Virtual Reality Check actually recommended 4 vCPU's at one point.

Fine for 2008 and up, not for 2003.

> This is acceptable assuming the terminal server is the only one with heavy load?

Should not a problem. If you reduce the vCPU for the TS to two, you don't even have CPU overcommit.
JamesNT Posted - 11/01/2011 : 12:48:10 PM
So, with CPU overcommit I can add another virtual machine with 2 vCPU's to have this:

2 for the host
4 for the 2003 terminal server
2 for the sql server
2 for the Exchange 2010 server
= 10 vProcs which accounts for all 8 cores (4 cores per proc) with an overcommit of 2

This is acceptable assuming the terminal server is the only one with heavy load?

JamesNT
JamesNT Posted - 11/01/2011 : 12:42:47 PM
wkasdo,

I may need to give overcommit a second look. I only need to add an Exchange Server to this machine and the Exchange along with SQL will sit on their butts most of the time.

Not in this case. Once I added the second pair of CPU's, people started reporting that their performanc lag went away.

Where is it documented that 2003 with 4 vCPU's is unsupported? The guys at Virtual Reality Check actually recommended 4 vCPU's at one point.

JamesNT
wkasdo Posted - 11/01/2011 : 12:39:07 PM
Let me qualify that last statement. Not only is 4 vCPU on 2003 unsupported, performance with 2 vCPU's might actually be better than a 4-vCPU 2003 VM.
wkasdo Posted - 11/01/2011 : 12:35:45 PM
> I have a server with two E5504 quad core procs. These procs are NOT hyper-threaded. The problem is that with two virtual machines and the host I am out of virtual processors.

Is there a problem with CPU overcommitment, i.e. using more vProcs than you have cores? http://blogs.technet.com/b/virtualization/archive/2011/04/25/hyper-v-vm-density-vp-lp-ratio-cores-and-threads.aspx

It's a good way to better utilize the full CPU power of the host. The flip side of this configuration is that you can max out the physical CPU, limiting performance.

> 4 for the 2003 terminal server

That's unsupported. Windows 2003 should have 1 or 2 vCPU's. There, I just gave you 2 vCPU's back ;-)
jaxdave Posted - 11/01/2011 : 12:13:45 PM
Not long ago it wasn't the best practice but with today's new processors always turn it on as Ton suggested.
Playwell Posted - 11/01/2011 : 12:12:44 PM
The article does not contradict me luckily :)
JamesNT Posted - 11/01/2011 : 11:49:22 AM
Found this:

http://www.windowsitpro.com/article/virtualization/q-does-hyper-threading-affect-hyper-v-

JamesNT
Playwell Posted - 11/01/2011 : 11:44:19 AM
It's always advisable to turn on hyperthreading.

A core with hyperthreading is like a small highway. 2 small cpu payloads can run parallel and pass each other, but for big payloads you have to wait until the payload takes an exit.

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