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Query around SQL Server Hyperthreading

on Sep 20, 2017
Latest reply on Oct 10, 2017 by Angelique

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Hello,

Was just wondering if any of you have had any experience with the following situations that i find myself in around SQL..

The problem I'm faced with is that our SQL servers are Virtual Machines so have a Virtual OSE, say for example we have "VM1" which has 4 Virtual Cores using the Per Core model i would need 2 core packs which would cover them...

Now we have hyper threading turned on so according to Microsoft this changes the requirement slightly so taking our "VM1" which has 4 VC if it is using 2 hardware threads then this will mean that the license requirement goes from 2 Core packs to being 3 Core packs..the extra 2 cores covering the two hardware threads which are providing the power to the 4 VC on "VM1"...

Common sense to me says that "VM1" which has been allocated 4 Virtual Cores at the setup stage to the Virtual Machine creation...will only ever have 4 VC at any time unless it is manually changed. So whether the VM has hyper-threading switched on or off will never change the fact that the VM will always have 4 VC..

Just wondered if any of you guys have come across a similar conundrum.

Any help would be appreciated!

Kind Regards,

Harry

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emmanuel.rasamoely

Sep 20, 2017 8:18 AM

Hello harry.mansell,

Hyper Threading does not affect the licensing of VM's. Each VM require a minimum of 4 SQL server core licences

Hyper Threading allow a HOST computer to have more SQL Server instances deployed, but in this case, you can consider to cover PHYSICAL Cores of the Host computer. (only with SQL Server Enterprise Licences, Standard not allowed)

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harry.mansell

@ emmanuel.rasamoely on Sep 21, 2017 4:28 AM

Morning Emmanuel,

Thanks for the response, I've attached a diagram which hopefully you can see what i mean.

The ESX hosts are both physical, and the Virtual Machine #1 is a VM with 4 Cores with hyper-threading switched on, how it works is that each set of Virtual Cores is powered by a different ESX hosts.

Microsoft's guidelines on SQL Server 2016 Virtualization and hyper-threading state:

"For customers using Intel’s hyper-threading technology to split a single, physical core into two separate
threads of power, there are some additional factors that should be kept in mind when licensing individual VMs
using the Per Core Model.
1. When hyper-threading is turned on, a core license is required for each thread supporting a virtual core. In
the example below, hyper-threading is enabled for the physical processor supporting a VM. Since hyperthreading
creates two hardware threads for each physical core, a total of 8 core licenses would be required
in this scenario. A core license allows a single virtual core to be supported by a single hardware thread.
2. Conversely, if a single hardware thread is supporting multiple virtual cores, a core license is still required for
each virtual core."

My understanding of this is that Microsoft want us to cover not only the 4 cores on the VM but also the 2 hardware threads from the different ESX hosts, which would mean a need for 2 more Cores...

The virtual machine has been setup with 4 CPU's, this isn't going to change automatically and will need human interaction to change the CPU's. So i don't understand why we should have to fork out more money to cover the fact that we are using hyper-threading..

Cheers

Harry

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emmanuel.rasamoely

@ harry.mansell on Sep 21, 2017 5:24 AM

See below the VMware point of view:

Hyper-threading doesn't count for virtual SQL licensing - Virtualize Business Critical Applications - VMware Blogs

I'm agree with this.

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harry.mansell

@ emmanuel.rasamoely on Sep 21, 2017 6:01 AM

Hey Emmanuel,

Yep that is what i found around the subject, and logically makes sense but have to be cautious as it's not a Microsoft piece!

Still interested to see if any other people have come across a similar issue?

Cheers

Harry

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dhardy

@ harry.mansell on Oct 2, 2017 3:24 AM

Hi Harry,

We have been in the same position as you and the advice we got is that the MS line has to be complied with. What we ended up doing was to build a VMcluster for SQL and disabled hyper-threading within this cluster so we only need to apply the basic rules. I know its not always possible to do this so in another environment of ours we have brought the extra licenses to cover hyper-threading.

Regards

Duncan

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Angelique

@ dhardy on Oct 10, 2017 10:43 AM

Read into it what you like but in a recent audit we were asked about hyperthreading and had to declare for each server:

whether hyperthreading is enabled
Total Number of Physical Cores or Threads per Physical Host

in addition to the usual VM and HPC questions

It would be good to get a Microsoft-based view on this...

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6 Replies

emmanuel.rasamoely Sep 20, 2017 8:18 AM
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Hello harry.mansell,
Hyper Threading does not affect the licensing of VM's. Each VM require a minimum of 4 SQL server core licences
Hyper Threading allow a HOST computer to have more SQL Server instances deployed, but in this case, you can consider to cover PHYSICAL Cores of the Host computer. (only with SQL Server Enterprise Licences, Standard not allowed)
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- harry.mansell @ emmanuel.rasamoely on Sep 21, 2017 4:28 AM
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  Morning Emmanuel,
  
  Thanks for the response, I've attached a diagram which hopefully you can see what i mean.
  
  The ESX hosts are both physical, and the Virtual Machine #1 is a VM with 4 Cores with hyper-threading switched on, how it works is that each set of Virtual Cores is powered by a different ESX hosts.
  
  Microsoft's guidelines on SQL Server 2016 Virtualization and hyper-threading state:
  "For customers using Intel’s hyper-threading technology to split a single, physical core into two separate
  threads of power, there are some additional factors that should be kept in mind when licensing individual VMs
  using the Per Core Model.
  1. When hyper-threading is turned on, a core license is required for each thread supporting a virtual core. In
  the example below, hyper-threading is enabled for the physical processor supporting a VM. Since hyperthreading
  creates two hardware threads for each physical core, a total of 8 core licenses would be required
  in this scenario. A core license allows a single virtual core to be supported by a single hardware thread.
  2. Conversely, if a single hardware thread is supporting multiple virtual cores, a core license is still required for
  each virtual core."
  
  My understanding of this is that Microsoft want us to cover not only the 4 cores on the VM but also the 2 hardware threads from the different ESX hosts, which would mean a need for 2 more Cores...
  
  The virtual machine has been setup with 4 CPU's, this isn't going to change automatically and will need human interaction to change the CPU's. So i don't understand why we should have to fork out more money to cover the fact that we are using hyper-threading..
  
  Cheers
  Harry
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  - emmanuel.rasamoely @ harry.mansell on Sep 21, 2017 5:24 AM
    Mark Correct
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    See below the VMware point of view:
    Hyper-threading doesn't count for virtual SQL licensing - Virtualize Business Critical Applications - VMware Blogs
    
    I'm agree with this.
    1 person found this helpful
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    - harry.mansell @ emmanuel.rasamoely on Sep 21, 2017 6:01 AM
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      Hey Emmanuel,
      
      Yep that is what i found around the subject, and logically makes sense but have to be cautious as it's not a Microsoft piece!
      
      Still interested to see if any other people have come across a similar issue?
      
      Cheers
      Harry
      1 person found this helpful
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      - dhardy @ harry.mansell on Oct 2, 2017 3:24 AM
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        Hi Harry,
        
        We have been in the same position as you and the advice we got is that the MS line has to be complied with. What we ended up doing was to build a VMcluster for SQL and disabled hyper-threading within this cluster so we only need to apply the basic rules. I know its not always possible to do this so in another environment of ours we have brought the extra licenses to cover hyper-threading.
        
        Regards
        Duncan
        3 people found this helpful
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        Angelique @ dhardy on Oct 10, 2017 10:43 AM
        Mark Correct
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        Read into it what you like but in a recent audit we were asked about hyperthreading and had to declare for each server:
        whether hyperthreading is enabled
        Total Number of Physical Cores or Threads per Physical Host
        in addition to the usual VM and HPC questions
        
        It would be good to get a Microsoft-based view on this...
        1 person found this helpful
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Query around SQL Server Hyperthreading

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