For the Virtual Storage Platform 5000 series, when creating a DP pool, you can set the subscription limit of the V-VOL capacity against the pool capacity. For details about the subscription limit, see the Provisioning Guide for your storage system.
When storing snapshot data in a DP pool, set the subscription limit of the V-VOL capacity against the DP pool by calculating the V-VOL capacity of a Thin Image pair (Thin Image pair capacity) using the following formula.
Thin Image pair capacity = Σ↑(P-VOL capacity (MB)
× Number of pairs × 2 ÷ 42 (MB))↑ × 42 (MB) + Σ↑(P-VOL capacity (MB) × Number of pairs
× 2 ÷ 2,921,688 (MB))↑ × 175,434 (MB)
Decimal places of the value enclosed by arrows (↑value↑) are rounded up.
As for Number of pairs in the formula, allocated pages are not released if you delete pairs. Because of this, use the maximum number of TI pairs you want to create in the applicable snapshot tree as Number of pairs instead of using the number of pairs currently created in the applicable snapshot tree.
If a pair or snapshot data is deleted, allocated pages are not released. As a result, if you delete pairs or snapshot data, the TI pair capacity is not decreased. To decrease the TI pair capacity by releasing allocated pages, you must delete all TI pairs and snapshot data created in the applicable snapshot tree.
The following example illustrates how the TI pair capacity is calculated.
When you create three TI pairs using the 500 GB (500 x 1024 MB) volume as the P-VOL, the TI pair capacity is calculated as follows:
↑(500 × 1,024 × 3 × 2 ÷ 42)↑ × 42 + ↑(500 × 1,024 × 3 × 2 ÷ 2,921,688)↑ × 175,434 ＝ 3,422,874 (MB)
Afterward, if you delete two pairs, the maximum number of TI pairs you can create in the applicable snapshot tree is the same: The TI pair capacity does not change.
Also, if you you split pairs twice, the maximum number of TI pairs you can create in the snapshot tree is the same, and the TI pair capacity remains unchanged.