Creating parity groups, LDEVs, and pools

If you have confirmed that saving on the used pool capacity is effective, create accelerated compression-enabled parity groups, LDEVs, and pools by following the workflow shown below. However, if saving on the used pool capacity is not effective, do not perform the operations described in this section.

The following describes the steps in the figure:

1. Check if a new FMC module is purchased.

If yes, go to Step 3.

If FMC is already used, go to Step 2.

2. Enable the accelerated compression function for an existing parity group.

In the Edit Parity Groups window, enable the accelerated compression function.

3. Use the purchased FMC capacity to create an accelerated compression-enabled parity group.

In the Create Parity Groups window, create a parity group.

4. Create LDEVs to be used as pool-VOLs.

Use the Create LDEVs window to create LDEVs. We recommend the capacity of a single LDEV to be 2.99 TB, which is the maximum capacity of a pool-VOL. Use the following formula to calculate the recommended value of the total LDEV capacity to be defined for one parity group:

Total LDEV capacity = FMC capacity of the parity group ÷ (100 [%] - (Saving rate [%] - 10 [%])) ÷ 110[%]

The values of the margins in the above formula are as follows:

• - 10[%]: Margin representing the expected increase in capacity because of degradation in saving

• ×110[%]: Margin representing the expected increase in capacity for storing the management information of the storage system

For example, assuming that a 3.2 TB FMC is used in a 3D + 1P configuration and the estimated saving rate is 40%, the number of required LDEVs is calculated by performing the following procedure:

1. Calculate the total capacity of the LDEVs to be created.

9.6 TB ÷ (100% - (40% - 10%)) ÷ 110% = 12.5 TB

2. Calculate the number of LDEVs.

If the capacity of an LDEV is 2.99 TB, 5 LDEVs are required.

ceil (12.5 TB / 2.99 TB ) = 5

The value enclosed in ceil( ) must be rounded up to the nearest whole number.

 If you use multiple parity groups, we recommend you configure the same basic usable capacity expansion rate for each parity group. Also, use the following formula to calculate the basic usable capacity expansion rate of the parity groups:

Basic usable capacity expansion rate of the parity groups = Total capacity of the LDEVs created from the parity groups ÷ FMC capacity of the parity groups

5. Create a pool or expand a pool.

After you create or expand a pool, add all of the created LDEVs to the pool.

 If any LDEVs cannot be added to the pool, this might be because data restoration for the drive failure failed. Make sure that all of the LDEVs are registered to the pool. If an LDEV cannot be added to the pool, in the event of drive failure, the LDEV will be included in the restoration targets when data is restored to a replacement FMC. In this situation, because the data size of the LDEV to be restored is larger than the size before restoration, the FMC capacity to be used for copying data might be depleted, causing data restoration to fail.

Add all of the LDEVs that were created from a single parity group to the same pool.