Cisco Rack for ESX Host

[iskoy.istem]

Hi Everyone,

can you help me size up a rack server for an ESX deployment. existing servers:

4 units servers w/ dual CPU (quad-core 2.0 GHz) and 8 GB RAM

can i just use dual 2.5 GHz 6C CPU w/ 64 GB RAM? this will total to 24 logical CPU w/ HT enabled.

calculating the existing CPU cores on the existing servers, it will add up to 32 CPU cores. Will CPU overcommitment be ok?

[Robert Burns]

CPU is usually not the first resource to limit scaling, but rather memory is.  I would say the replacement builds you're looking for will offer a definate performance improvment.

Keep in mind when sizing your hypervisor hosts, you dont necessary need to just look at your existing hardware.   The main factor should be your application requirements now and in the next 2-3 years to ensure you get a full lifespan from your spec'd hardware.  Rack servers are relatively cheap compared to the performance cost if you're running into over commit issues in the next 12 months.

Regards,

Robert

[iskoy.istem]

hi Robert,

please clarify if overcommitting on the cpu core is ok as long as total CPU cycle load is just around 80 percent. even though i use around 32 vCPU with only 12 physical CPU available on a host, as long as i don't over the 80% of the total CPU cycles, my host should be fine?

i understanding, usual limiting factor is on the memory. my allocated memory is around 64GB which i think would be more than enough.

[Robert Burns]

I would be careful there.  One quesiton to ask is do your VMs need more than a single CPU?  Many people inadvertingly think that by giving their VMs multiple vCPUs that performance will be directly improved.  The way the hypervisor scheduler works allows the VMs to take advantage of all the CPU power of the host.  when you define a VM with multple CPUs (Say 4), the kernel has to wait for 4 physical CPUs to become availalbe to process the requests.  Unless you specifically have multithreaded applicaitons, often keeping VMs with the default 1 vCPU will offer the best performance & balance. 

I would say its fine to overcommit CPU to an extend, but I wouldn't go any further 1.5x myself, but maybe others can speak to their experience specifically regarding CPU over commit levels.

Regards,

Robert

[iskoy.istem]

hi robert,

thank you for this insights. those information aren't taught on VMware ICM i guess?

considering those inputs, i really need to understand the applications running on the physical server of the client if it's single or multi-threaded apps.

[Jeremy Waldrop]

Post install you can use VMware vCOPS Advanced to find over provisioned VMs. These reports are handy to show app owners and management that they really don't need 4 vCPUs and 16G RAM.