hesela.devEffective capacity
Effective capacity, under the SNIA convention, combines stored logical data with remaining formatted capacity.
Accounting: Space optimization can let the logical data represented exceed its physical footprint. The SNIA measure adds that stored data to unused formatted capacity; it does not assume the unused part will achieve the current reduction ratio. [1]
Forecast: Multiplying total usable capacity by an observed reduction ratio is a different, conditional estimate. Future data and retained versions can change the ratio. Neither figure is a reservation of backing space. Product counters require their own documented accounting scope. [1] [2]
Planning: Keep current accounting separate from a future-workload budget and from policy headroom. In a hypothetical pool with 60 TB logical stored in 30 TB and 70 TB free, leaving 10 TB unused gives a 60 TB physical growth budget. An incoming 1.6:1 mix adds 96 TB logical, versus 120 TB at the old 2:1 ratio under the same headroom. The policy is not an enforced reservation. After that modeled addition, the new SNIA snapshot is 156 + 10 = 166 TB, not the original 130 TB.
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Sources & caveats
- Terminology follows the cited accounting convention; no storage-array measurement or capacity guarantee is implied.