View Clients limitations for CPU

[Davidedwards122]

I  am starting a VDI POC for a small group of users (8), to  keep my  costs low I  have used an older ESX host (3 years old  previously used to support 15 - 20 servers)  which  has 2 Processors and 4 cores each processor, the machine has 48GB RAM 1TB Storage  raid 5, disk are new 15k disks and are local storage for the POC..

We have installed the required server components using 3 virtual CPU.

We have created an optimised windows 7  image through the composer and created the pool etc. The feedback from the engineer is I can only support 5 clients as I only have 5 virtual CPU's left (4 cores *2 - 3).

I  this really true does as this  does not seam correct, I  would have expect  to support many connections and the performance would just reduce, not have physical limit based on CPU  ?

Can some help explain to be why he might say this ?

Thanks

[dpain · Accepted solution]

Hi,

Most consultants usually recommend 7 or so desktop VM's per CPU core, so you would be able to have lots more users than 5!  Obviously it all depends upon the workload of each desktop VM.  If it's just Office applications and Internet browsing maybe 10 VM's per core. Memory is a bigger factor than CPU power though; just be aware that if your Win7 desktops have 3 or 4GB each you'll soon find yourself hitting that 48GB RAM ceiling, even with transparent page sharing.

Common practise is to use Win7 x86 instead of x64 and it's lighter on memory usage.

Regards,

Darren V Pain

VCP, VCA-DT, VCP-DT, MCITP

www.freestyle-it.co.uk

[TomHowarth]

As a rule of thumb, it is best to keep your CPU over commit as low as feasable, however a overcommit rate of 5 VM's per Core is not excessive,  in my experiance you are more likely to run into issues with your Memory as 48GB is quite low.  if you are running Windows 7 images you will really need at least 2GB to make them run at a sensible level, and if you are using HDX or higher graphics resolutions then you will obviously also have to increase your Guest memory.  Another limiting factor may be the Network connectivity and also the Storage.  A VDI Guest is quite IO intensive especially on Writes a windows does make signficant use of Memory swap.

[jawadqazi]

I second Tom, an overcommit ratio of 5 VMs per core is an ideal solution for infrastructures of these days, as the graphics of OS and applications running on them has increased extensively. The minimum requirement of a normal Win7 OS with standard office apps use 2 GB memory, so if the physical memory on the host suffices your requirement then 5 VMs per core is perfect.

By this calculation your host can run 20-22 VMs with standard apps.