Inspiration is coming from word “Let’s challenge”, If I know something then I must be in a position to explain it well and how much well I know, it would be seen in the comments. So here is design requirement, create virtual farm for 40 Virtual Machines with each 2GB RAM.This is strict requirement.
Total RAM Required
40 VM’s X 2GB (RAM) =80 GB RAM
Design best practice is to keep 4GB/Core (Reference: Advanced Technical Design Guide (Ron Oglesby, Scott Herold and Mike Laverick)
So we will need 20 Cores (80/4=20)
I chose 8 core machine i.e. 2 Way Quad Core machine (is explained in next blog)
8 Cores and 4GB/Core, I can easily host 32 GB RAM in total. So hardware will be 2 Way Quad Core and with 32 GB RAM
Total Number of Virtual Machines
Taking 4GB/Core and 2GB requirement for each VM, We can host only 2 VM’s/core.
So 2(VM’s/Core) X 8(Core) =16 VM
Out of total compute capacity let’s reserve 10% for service console, VMKernel and other host management agent.
10% of 32GB RAM comes to =3.2 GB RAM approx 4GB (I know very high amount)
So we are left to manipulate only 28 GB RAM (32 – 4 ) i.e. 4GB RAM less which means 2 VM’s less.
So by this calculation we can host safely(Very Very) 14 VM’s/Host.
Total Number of Host
We are asked to host 40VM’s.
40 (VM’s)/14 (VM’s /Host)=2.8 approx #3 Hosts
14 (VM’s/Host) X 3 (Hosts) =42 Total virtual machines
And to consider a failover capacity of one host, we can add one more host.
Total number of host will be 4 with one host failover capacity. Failover capacity will also take care of maintenance activity like patches
So total Memory resources =32GB RAM X 4 host =128 GB RAM
VM’s/ Host=40/4=10 VM
If one host fails, 3 host will be able to accommodate 40 virtual machines i.e. 40/3=13 VM’s host.(We designed 14/host, which means we can add 2 more VM’s)
This is one min design guide. There are still many parameters to consider. Definitely if we need to consider over committed benefit through TPS,Ballooning, I think we can add more VM to this 4 node cluster. But how many more VM, that is topic for next blog.