Workflow for creating parity groups, LDEVs, and pools with accelerated compression

When you have confirmed that the Saving % on used pool capacity is sufficient, use the following workflow to create accelerated compression-enabled parity groups, LDEVs, and pools.

1. Check whether FMC parity groups are already used.

If yes, go to step 2.

If no, go to step 3.

2. Enable the accelerated compression function for an existing parity group. Use the Edit Parity Groups window to enable accelerated compression.

3. Use the new FMC capacity to create accelerated compression-enabled parity groups. Use the Create Parity Groups window to create parity groups.

4. Create LDEVs to be used as pool-VOLs. Use the Create LDEVs window to create LDEVs.

Best practice is to create 2.99-TB LDEVs because this 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 % - 10%)] ÷ 110%

The buffers in the formula are as follows:

• - 10%: Buffer representing the expected increase in capacity used because of degradation in the Saving %

• ÷ 110%: Buffer representing the expected increase in capacity used to store management information of the storage system

If the 14-TB FMC is used and the Saving % exceeds 75%, apply 75% for "Saving %" in the formula for total LDEV capacity.

For example, when the 3.2-TB FMC is used in a 3D+1P configuration and the estimated Saving % is 40%, the number of required LDEVs is calculated as follows:

• Calculate the total capacity of the LDEVs to be created as follows:

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

• Calculate the number of LDEVs as follows. The value enclosed in ceil( ) must be rounded up to the nearest whole number.

ceil(12.5 TB ÷ 2.99 TB ) = 5

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

If you use multiple parity groups, best practice is to configure the same basic usable capacity expansion rate for each parity group. 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 or expand the pool, and then add all of the created LDEVs to the pool.

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

• If LDEVs cannot be added to the pool, the cause might be that data restoration for the drive failed. Make sure that all 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.