Home > Storage > PowerMax and VMAX > Storage Admin > Dell PowerMax and VMware vSphere Configuration Guide > Thin device data reduction
On the PowerMax, inline compression is available. Compression on the PowerMax is hardware-based, with the ability to use software in case a failure occurs. Individual devices cannot be compressed, rather compression is enabled at the storage group level for all devices within the group. Data is compressed as it is written to disk when the device is in a storage group with compression enabled. If compression is enabled on a storage group that already has data, a background process compresses that data. If compression is disabled on a storage group, new written data is not compressed but existing data is not immediately decompressed. Only when data is written again is it decompressed.
Note: Preallocated persistent devices cannot be compressed.
Note: Data reduction is not applicable on data that is stored on Storage Class Memory (SCM).