Because qtree SnapMirror operates at the logical level, when data compression is enabled on the source system, the data is uncompressed in memory before being replicated to the destination system. If data compression is enabled on the secondary system, then all transfers are compressed on the secondary system.
When data compression is enabled on the source volume, no bandwidth savings are achieved over the network because the data is uncompressed on the source volume before it is sent for replication. If inline compression is enabled on the destination volume, the data is compressed inline at the destination before it is written to the disk. If inline compression is not enabled on the destination volume, you must manually compress the data after the qtree SnapMirror transfer is completed to achieve storage space savings in the destination volume.
For more information about inline compression and how data compression works with qtree SnapMirror, see the Data ONTAP Storage Management Guide for 7-Mode.