Managing Deduplication Capacity

Deduplication cannot be enabled on a storage pool if, at the time the storage pool is created, the current deduplication capacity (CDC) is less than or equal to zero.

Deduplication can be enabled on the storage pool if, after the storage pool is created, the CDC becomes greater than zero. This setting persists regardless of the CDC.

A pool can only be marked deduplication-enabled if the following four factors are present:

  • The array type supports deduplication
  • The array is a Secondary Flash Array
  • The FDR is greater than 4% (the CDC is greater than zero)
  • The array has enough SSDs to support deduplication

A volume created in a deduplication-enabled storage pool can have deduplication set to Yes, regardless of the CDC level, provided the FDR is at least 4%. Newly written blocks will be deduplicated if the CDC is greater than zero and the capacity of deduplicated data is less than the CDC.

If the CDC is equal to zero, or the capacity exceeds the CDC, deduplication of new writes stops.

If you increase the CDC, deduplication will resume; however the data that was written while deduplication was disabled will not be deduplicated. When old data is overwritten the newly written data will be deduplicated.

The following are suggestions of how to manage deduplication capacity:

Condition Suggested Action
If the CDC is equal to the maximum deduplication capacity (MDC) Perform a controller upgrade, if possible
If the CDC is less than the disk capacity Add flash or unpin volumes
If the CDC exceeds the previous levels Add a shelf that has a flash deduplication requirement (FDR) of at least 4%