Taken from the user guide
Data CompactionDisplays the overall amount of storage space saved via HP 3PAR Thin Technologies. This is the amount of storage presented to the host versus how much has been reserved or used on the various virtual volumes.
Note thin technologies applies to a combination of techniques in a 3PAR array, potentially not just thin provisioning, that's why it's being termed compaction. But basically it's the space consumed on disk (total used space) vs what you would see with a fully provisioned (virtual size) volume.
A bit more data from here
http://h20195.www2.hp.com/v2/GetPDF.asp ... 987ENW.pdf page 19 onwards.
The capacity efficiencies of a base volume are shown by the showvv -space command and are calculated as follows:
The compaction ratio of a TPVV is the virtual size of the volume divided by the sum of its used admin space and its used data space.
The compaction ratio of a TDVV is the virtual size of the volume divided by the sum of its used admin space, its used data space and its used Dedup Store space.
The dedup ratio of a TDVV is the size of the data written to the TDVV divided by the sum of the data stored in the TDVV and the data associated with the TDVV in the Dedup Store.
