We have VMs with recommendation since using less than 20% CPU to lower CPU, is there risk?

Hello EE,

In my VM environment, we have a new storage system that tells us via reporting systems with less than 20% memory and CPU utilization.  The reports recommends to regain resources to lower these.  I understand the lowering memory, but for CPU, is there risk with lowering Cores per Sockets or Sockets (I'm not sure the difference) if I have 2 on both and they suggest going to 1
operationsITAsked:
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Lee W, MVPTechnology and Business Process AdvisorCommented:
Some people say start with 1.  I say start with and stay at 2 cores.  You're not assigning the resources exclusively, so it shouldn't cause a severe performance issue, especially if you have a lot of cores.  Why 2?  I've WAY too often seen operating systems that have a process that goes nuts and eats up CPU. When this happens, especially if there's only one core/cpu allocated to the system, it can make the system slow to unresponsive.  By allocating 2 cores/cpus, the system continues to be responsive and (hopefully you have configured) alerts you to a problem where CPU usage is excessive and unusual.
Lee W, MVPTechnology and Business Process AdvisorCommented:
I will add that more does not generally mean better - due to how the CPU time is allocated among VMs, it can actually cause performance issues with too many CPUs allocated to a VM - however, in general, *I* consider 2vCPU to be safe, especially on a system capable of 8 or more threads.
operationsITAuthor Commented:
Is there harm going from 8 to 2 if only 20% are in use?  How about with Memory?
Lee W, MVPTechnology and Business Process AdvisorCommented:
Harm?  It might IMPROVE performance if you reduce the CPU count!

Read http://www.zdnet.com/article/virtual-cpus-the-overprovisioning-penalty-of-vcpu-to-pcpu-ratios/

As for RAM,  VMWare is supposed to be able to overcommit RAM.  I don't use VMWare - I use Hyper-V.  But In general the more RAM the better.  But allocating it intelligently amongst the VMs is important.  Giving an RDS server 4 GB of RAM when practically, to support 10 users, it should have 16 while giving a file server 16 GB of RAM when practically it only needs 2-4 is a waste.  As a general rule, I allocate reasonable but conservative amounts of RAM to systems that generally don't need RAM and then divvy up the rest among systems that do.  DCs, File servers don't need much RAM, Databases and RDS servers do.  (Nice thing about Dynamic RAM in Hyper-V, it shows you what it's using and for small environments, File Servers and DCs do just fine with as little as 2 GB (I allocate 2 to start, minimum is 512 and maximum is 4GB).

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operationsITAuthor Commented:
Great article!
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