Understanding the Calculation Context:In PowerStore, capacity planning for virtualized environments involves forecasting storage requirements based on VM deployments. The formula VM count × Capacity per VM is specifically used to model projected storage consumption before applying efficiency factors.
PowerStore's Capacity Terminology:
Raw Capacity: The total physical capacity of installed drives before accounting for RAID overhead, system metadata, or formatting.
Usable Capacity: The available storage after subtracting RAID overhead, system partitions, and metadata. Represents the logical space presented to the user before data reduction.
Effective Capacity: The logical storage capacity available to applications after accounting for data reduction technologies (deduplication, compression), thin provisioning, and system efficiency. It represents the "logical" data stored per physical byte.
Why "VM count × Capacity per VM" Equals Effective Capacity:
Capacity per VM typically refers to the provisioned (logical) storage allocated to each VM (e.g., a 500GB virtual disk).
Multiplying this by the VM count gives the total logical capacity required by all VMs.
PowerStore uses this product to calculate the "Effective Capacity" requirement. This is the logical capacity the system must support after data reduction efficiencies are applied. It represents the total amount of data the VMs will logically store, which the physical storage (Usable/Raw Capacity) must ultimately hold after deduplication/compression.
Official Dell PowerStore Documentation:The Dell PowerStore: Deployment Planning and Best Practices Guide explicitly defines this calculation:
"Effective Capacity is calculated as: Number of VMs × Average Capacity per VM."
(Source: Dell PowerStore Deployment Planning and Best Practices Guide, Section: Sizing Considerations for Virtualized Environments)
This guide further clarifies that Effective Capacity is the key metric for sizing PowerStore systems in virtualized scenarios, as it represents the logical workload demand the system must satisfy, leveraging its data reduction capabilities to fit onto the physical Usable Capacity.
Conclusion:
Multiplying VM count by Capacity per VM directly yields the Effective Capacity requirement. This represents the logical storage demand placed on the PowerStore system. The physical Usable Capacity must be sufficient to hold this Effective Capacity after data reduction savings are applied. Raw Capacity is unrelated to VM provisioning calculations.
Key References:
Dell PowerStore: Deployment Planning and Best Practices Guide (Current Version) - Definitive source linking VM count × Capacity per VM to Effective Capacity.
Dell PowerStore: Introduction Guide - Explains core concepts of Raw, Usable, and Effective Capacity.
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