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Determining the impact to cache size of adding SSDs to an SSD storage pool

If adding SSDs to a storage pool causes your platform model's cache limit to be exceeded, Data ONTAP does not allocate the newly added capacity to any Flash Pool aggregates. This can result in some or all of the newly added capacity being unavailable for use.

About this task

When you add SSDs to an SSD storage pool that has allocation units already allocated to Flash Pool aggregates, you increase the cache size of each of those aggregates and the total cache on the system. If none of the storage pool's allocation units have been allocated, adding SSDs to that storage pool does not affect the SSD cache size until one or more allocation units are allocated to a cache.

Steps

  1. Determine the usable size of the SSDs you are adding to the storage pool: storage disk show disk_name -fields usable-size
  2. Determine how many allocation units remain unallocated for the storage pool: storage pool show-available-capacity sp_name
    All unallocated allocation units in the storage pool are displayed.
  3. Calculate the amount of cache that will be added by applying the following formula:

    ( 4 – number of unallocated allocation units) × 25% × usable size × number of SSDs