Virtual Kim

@Kim_Bottu … Virtually Gung Ho

BASIC CALCULATIONS

CALCULATE THE NUMBER OF HOSTS NEEDED

How many hosts does the client need to host all the VMs? The client wants N + 1 redundancy to be maintained at ALL times.

The client has 1000 VMs. Each VM has:

  • 2 cores
  • 2 GHz per core
  • 4GB of RAM

The client wants to purchase Physical hosts with the following resources:

  • 2 sockets and 5 cores
  • Each core has 20 GHz
  • 192 GB of RAM

——————————–

Total resources needed for 1000 VMs:

  •  2 (cores)* 2(GHz) * 1000 (VM) = 4000 GHz 
  • 1000 (VM)  * 4 (GB) = 4000 GB of RAM

Available resources per hosts for VM’s = 80% of available physical resources!

  • {2 (sockets) * 5 (cores) * 20 (GHz)} * 80% = 160 GHz
  • 192 GB * 80% = 153.8 GB

Amount of hosts needed:

  • 4000 GHz / 160 GHz =  25 Hosts for CPU requirements
  • 4000 GB / 153.6 GB = 27  Hosts for RAM requirements

Because you need 27 Hosts to fulfill the RAM requirements, this is the amount of hosts which = N.

For N + 1 you need to add 1 host:  28 Hosts. But the exercise states that N + 1 has to be maintained at all times, which mean N +1 has to be maintained even in Maintenance! A host in maintenance does not participate in failover capacity so you have to add 1 more host = 29 HOSTS!

Note: Suppose one of your calculations = a number higher than the maximum number of hosts per Cluster,for example 70. Each cluster would have 35 Hosts as N. Each cluster would need 37 Hosts to comply with the requirements to have N +1 redundancy at all times. Changing a host to a different cluster might not be something you want to do, it takes a lot of time and in some cases is not that easily done.

 

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