Understanding Cluster Cost Computation Allocation Model Cost Formulas for vCPU, vRAM, and Storage in VMware Aria Operations

Products

• VCF Operations/Automation (formerly VMware Aria Suite)

Issue/Introduction

Manual calculations don't match the values displayed on Aria Operations Metrics:

vCPU base rate = B1 = (Cost attributed to CPU) / (Number of vCPUs in a cluster)  

RAM base rate = B2 = (Cost attributed to RAM) / Number of vRAMs in a cluster)

Environment

VMware Aria Operations 8.18.x

Cause

Discrepancies between the UI output and manual calculations are typically caused by one or more of the following configuration oversights:

• Inaccurate Source Metrics: Applying a uniform, flat cost to all servers in manual calculations instead of using the actual individual hardware costs (e.g., assuming all servers cost 35,550 when some cost 32,695).

• Missing Allocation Ratios: Failing to account for the specific over-allocation ratios (e.g., 4:1) defined in the active policy.

• Incorrect Buffer Settings: The active policy having an incorrect Capacity Buffer percentage. For example, entering a 99% buffer when the actual intent is a 0% buffer (100% capacity utilization). This drastically alters the system's expected capacity adjustments and skews the base rate.

 

 

Resolution

For accurate manual reconciliations, use the detailed formulas below, which explicitly account for the Over-Allocation Factor and buffer capacity.

1. Cluster CPU Base Rate

• Metric Key: cost|allocation|allocationBasedCpuBaseRate (currency/vCPU/month)

• Formula:
  
  Cluster CPU Base Rate = (Cluster Total CPU Cost) / (Total CPU Cores × CPU Over-Allocation Factor)

• Cluster Total CPU Cost: Sum of all server CPU monthly costs in the cluster.

• Total CPU Cores: Total number of physical CPU cores across all servers in the cluster.

• CPU Over-Allocation Factor Logic: Calculated based on the actual allocation ratio (allocated vCPUs / total physical CPU cores).

  • If allocation ratio less than or equal to 4: Returns the next power of 2 (e.g., 1, 2, 4).

  • If allocation ratio is between 4 and 6: Returns 6.

  • If allocation ratio greater than 6: Returns the ceiling value of the ratio.

• Note: The CPU base rate is adjusted based on the configured CPU buffer capacity (expected utilization percentage) if set.

2. Cluster Memory Base Rate

• Metric Key: cost|allocation|allocationBasedMemoryBaseRate (currency/GB/month)

• Formula:

  Cluster Memory Base Rate = (Cluster Total Memory Cost) / (Total Memory Capacity GB × Memory Over-Allocation Factor)
  
  

• Cluster Total Memory Cost: Sum of all server memory monthly costs in the cluster.

• Total Memory Capacity (GB): Total physical memory capacity across all servers in the cluster.

• Memory Over-Allocation Factor: Calculated as the ceiling of the memory allocation ratio.

Additional Information

Cluster Cost Computation with Allocation Model