Data compression enables you to store more data in less space. Further, you can use data compression to reduce the time and bandwidth required to replicate data during volume SnapMirror transfers. Data compression can save space on regular files or LUNs.
However, storage system internal files, Windows NT streams, and volume metadata are not compressed.
If inline compression is enabled on a volume, during subsequent data writes the compressible data is compressed and written to the volume. However, data which cannot be compressed or data bypassed by inline compression is written in the uncompressed format to the volume.
If postprocess compression is enabled on a volume, the new data writes to the volume which were not compressed initially (if inline compression is enabled), are rewritten as compressed data to the volume when postprocess compression is run. The postprocess compression operation runs as a low-priority background process.
If both inline and postprocess compression are enabled, then postprocess compression compresses only the blocks on which inline compression was not run. This includes blocks that were bypassed by inline compression such as small, partial compression group overwrites.