Estimating FMD capacity for a new pool

When you need to install FMD drives to create a new pool, use the following workflow to estimate the required capacity.

Note

To estimate the FMD capacity to be used for an accelerated compression-enabled parity group, estimate a buffer capacity in addition to the main capacity for storing data. Add approximately 20% of the required FMD capacity as buffer capacity. Buffer capacity refers to the total expected increase in FMD capacity, which includes the following:

  • Expected increase in capacity used to store management information of the storage system
  • Expected increase in capacity to offset degradation of the Saving % compared with estimated values

  1. Estimate the required pool capacity.

    Estimate the pool capacity required for user data in the same way you estimate capacity when creating a pool. If you are expanding a pool, also estimate the pool capacity required for user data.

  2. Estimate the Saving % using one of the following methods:
    • If data will be migrated to the FMD, use the Compression Estimator Tool to estimate the Saving %. The tool reports a Saving % that can be used to determine the capacity needed. If the estimate is less than 20%, best practice is to use a parity group with accelerated compression disabled, and to estimate the pool capacity by the conventional method.

    • If new data will be stored on the FMD, or if the Compression Estimator Tool cannot be executed in the environment, consider setting the Saving % to 0% and using the conventional method to size capacity. With accelerated compression disabled for the parity group, you can monitor the Saving % through the management software and then decide to enable accelerated compression at a later time.

    NoteIf the 14-TB FMD is used and the Saving % that is estimated in this step exceeds 75%, apply 75% for "Saving %" in the formula of the next step.

  3. Estimate the required FMD capacity to be purchased.

    If there is data to migrate to the FMD, use the following formula to calculate the required FMD capacity. 

     Required FMD capacity to be purchased = 
			 required-pool-capacity * (100% - (Saving % - 10%)) × 110%

    The buffers in the above formula are as follows:

    • - 10%: Buffer representing expected increase in capacity because of degradation in Saving %
    • * 110%: Buffer representing expected increase in capacity because of additional space required to store management information of the storage system

    Then, enable accelerated compression and create parity groups, LDEVs, and pools.

    Note

    When using Dynamic Tiering or active flash, if the Tier 1 is configured of FMD drives, use 1.2 times the calculated required pool capacity. Use the following formula to calculate the value: 

     Required pool capacity = 
				required-pool-capacity-estimated-in-Step-1 × 120%

    To prevent the depletion of assured capacity for writing due to the tier relocation, Dynamic Tiering or active flash uses a 20% buffer when calculating the number of pages that can fit in the FMD tier. If accelerated compression is disabled, Dynamic Tiering or active flash do not use the 20% buffer.

    Therefore, if the same FMD (Tier 1) capacity is applied, the amount of data that can be stored with accelerated compression enabled is smaller than the amount of data that can be stored with accelerated compression disabled.

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