Estimating FMD capacity to expand an existing pool

When you need to install additional FMD drives to expand an existing pool, use the following workflow to estimate the required capacity.

1. Estimate the pool capacity to be added.

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

2. Check the Saving %.

   The Saving % is displayed in the Pools window. View the Saving % by clicking Pools FMD Pool Volumes Capacity Saving (%).

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

3. Estimate the required FMD capacity.

   Use the following formula to calculate the required FMD capacity:

   Required FMD capacity = Required pool capacity × [100% - (Saving % - 10%)] 
   		  

   The buffer in the above formula is as follows:

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

   Estimate the additional FMD capacity to be purchased according to the required FMD capacity calculated using the above formula, and the free capacity assured for writing.

4. Check the free capacity assured for writing.

   In the Pools tab of the Pools window, check the value of FMD Pool Volumes Capacity. The free capacity reserved for writing is the difference between the Total and Used values.

5. Estimate the additional FMD capacity to be purchased.

   If the space calculated in step 4 is sufficient, this step is unnecessary. If the space is insufficient, use the following formula to calculate the required FMD capacity:

   Required FMD capacity to be purchased = (Required FMD capacity - free capacity assured for writing in step 4) × 110% 
   		  

Parent Topic

• Estimating required FMD capacity