Before creating a pool, you need to estimate the pool capacity. First calculate the amount of snapshot data to be stored, and then calculate the required capacity for Thin Image Advanced pairs based on the amount of snapshot data. You need to set the pool capacity large enough to accommodate that capacity.
Use the amount of data written from hosts to the Thin Image Advanced pair per specified time and the retention period between the time the snapshot data is created and the time the snapshot data is deleted. Calculate the amount of snapshot data to be stored, according to the following formula:
Amount-of-snapshot-data-to-be-stored = (average-amount-of-host-write-data × retention-period-of-snapshot-data)
Calculate the value for retention-period-of-snapshot-data as in the following example.
Example:
If you store snapshot data once a day and retain 7 pairs, the retention period is 7 days. If the average amount of host write is 100 GB a day, 700 GB (100 GB/day x 7 days) is obtained as the amount of snapshot data to be stored.
Use the following formula to calculate the capacity for a Thin Image Advanced P-VOL. To calculate the capacity for all Thin Image Advanced P-VOLs, total the capacity for each P-VOL.
capacity-for-a-Thin Image Advanced-pair =
(capacity-defined-for-the-root-volume + amount-of-snapshot-data-to-be-stored) x (1.13 - 1.07 x capacity-saving-rate) + (capacity-defined-for-the-root-volume x number-of-pairs) x 0.00016
Example:
When the capacity defined for the root volume is 5 TB, the amount of snapshot data is 0.7 TB, the capacity saving rate is 0.5 (50%, capacity saving ratio 2:1), and the number of pairs is 100:
Capacity-for-Thin Image Advanced-pair
= (5 TB + 0.7 TB) x (1.13 - 1.07 x 0.5) + (5 TB x 100) x 0.00016
= 5.7 TB × 0.595 + 500 TB x 0.00016
= 3.3915 TB + 0.08 TB
= 3.47 TB