OceanStor Dorado V6 Capacity Calculation Algorithm

Available nominal capacity of a single disk = Nominal capacity of a single disk – (512 MiB + 65 MiB) – 2 GiB

512 MiB and 65 MiB are reserved for disk authentication (512 MiB is the main reservation and 65 MiB is for backup). In addition, 2 GiB is reserved on each disk for coffer space.

Usable capacity = [Total available nominal capacity of single disks x (1 – Reserved capacity proportion) x (1 + Compensation capacity proportion) – Hot spare capacity] x RAID utilization

The reserved capacity proportion includes garbage collection and metadata ratios. The specific value depends on the disk type.

RAID utilization = (Total number of RAID columns – Number of RAID parity columns M)/Total number of RAID columns

Total number of RAID columns = MIN(Disk quantity – IF(Hot spare disk quantity = 0,1,Hot spare disk quantity),N)

N：

Number of RAID parity columns M:

Rules:

Capacity compensation has two grades:

• Threshold 1 (cap1): 6 TiB. The compensation ratio is 14.6% (ratio 1).
• Threshold 2 (cap2): 20 TiB. The compensation ratio is 2% (ratio 2).

If the total usable capacity excluded by the reservation ratio is totalCap, totalCap = Total available nominal capacity of single disks x (1 – Reservation ratio)

• If totalCap > cap1, calculate the compensation capacity in phase 1: compensateCap1 = (totalCap – cap1) x Ratio 1
• If totalCap > cap2, calculate the compensation capacity in phase 2: compensateCap2 = (totalCap – cap2) x Ratio 2
• Calculate the average capacity compensation ratio:averageRatio = (compensateCap1 + compensateCap2) / totalCap

Hot spare disk quantity ranges from 0 to 8.

Constraints: Number of disks – Hot spare disk quantity ≥ 5 (minimum number of RAID columns)

Hot spare capacity = [Hot spare disk quantity x Available nominal capacity of a single disk x (1 – Reserved capacity proportion)] x (1 + Compensation capacity proportion)

Effective capacity = Usable capacity x Data reduction ratio

1. Available nominal capacity of a single disk

   Available nominal capacity of a single disk = (3840 GB x 1000 x 1000 x 1000/1024/1024) – 512 MiB – 65 MiB – 2 GiB = 3659484.375 MiB = 3573.715209 GiB

2. RAID utilization

   Total number of RAID columns = MIN(Disk quantity – IF(Hot spare disk quantity = 0,1,Hot spare disk quantity),25)
   RAID utilization = (Total number of RAID columns – Number of RAID parity columns M)/Total number of RAID columns = (25 – 2)/25

3. Compensation capacity proportion

   totalCap = 30 x 3573.715209 x (1 – 20.5%) = 85233.10773465 GiB
   compensateCap1 = totalCap – 6 TiB = (85233.10773465 GiB – 6144 GiB) x 14.6% = 11547.0097292589 GiB
   compensateCap2 = totalCap – 20 TiB = (85233.10773465 GiB – 20480 GiB) x 2% = 1295.062154693 GiB
   averageRatio = (compensateCap1 + compensateCap2)/totalCap = (11547.0097292589 GiB + 1295.062154693 GiB)/85233.10773465 GiB = 15.06%

4. Hot spare capacity

   Hot spare capacity = Hot spare disk quantity x Available nominal capacity of a single disk x (1 – Reserved capacity proportion) x (1 + Compensation capacity proportion) = 1 x 3573.715209 x (1 – 20.5%) x (1 + 15.06%) = 3268.973791982943 GiB = 3.192 TiB

5. Usable capacity

   Usable capacity = [Total available nominal capacity of single disks x (1 – Reserved capacity proportion) x (1 + Compensation capacity proportion) – Hot spare capacity] x RAID utilization = [(3573.715209 x 30) x (1 – 20.5%) x (1 + 15.06%) – (3573.715209 x 1) x (1 – 20.5%) x (1 + 15.06%)] x (25 – 2)/25 = 87216.22077010492 GiB = 85.172 TiB

6. Effective capacity

   Effective capacity = Usable capacity x Data reduction ratio = 85.172 x 2 = 170.344 TiB