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# Understanding data reduction

Data reduction allows users to reduce user data on storage groups and storage resources.

Data reduction is enabled by default and can be turned on and off at storage group and storage resource level.

If a storage group is cascaded, enabling data reduction at this level enables data reduction for each of the child storage groups. The user can disable data reduction on one or more of the child storage groups.

To turn the feature off on a particular storage group or storage resource, clear the Enable Data Reduction check box in the Create Storage Group, Modify Storage Group, or Add Storage Resource To Storage Container dialogs or when using the Provision Storage or Create Storage Container wizards.

The following are the prerequisites for using data reduction:

- Data reduction is only allowed on All Flash systems running the HYPERMAX OS 5977 Q3 2016 Service Release, or PowerMaxOS 5978, or greater.
- Data reduction is allowed on FBA and CKD devices.
- The user must have at least StorageAdmin rights.
- The storage group must have an associated SRP.
- The associated SRP cannot be comprised, either fully or partially, of external storage.

## Reporting

Users can see the current data reduction ratio on the device, the storage group, and the SRP. Efficiency ratios are reported in units of 1/10:1.

| NOTE: External storage is not in efficiency reports. Mixed SRPs with internal and external storage, only the internal storage is used in the efficiency ratio calculations.