How qtree SnapMirror works with data compression

Because qtree SnapMirror operates at the logical level, when data compression is enabled on the source storage system, the data is uncompressed in memory before being replicated to the destination system. If data compression is enabled on the secondary storage system, then all transfers are compressed on the secondary storage system.

You can use data compression to compress any existing data on the secondary storage system.

When using qtree SnapMirror with data compression, consider the following guidelines:

• If you want to compress data on your source volume, you must enable data compression on the source volumes.
• If you want to compress data on the destination storage system, you must enable data compression on the destination volume.
• When data compression is enabled on the source storage system, blocks are sent as uncompressed data to the destination storage system.

  Therefore, no network bandwidth savings are achieved by data compression.

• You can enable data compression on the destination storage system even if it is not enabled on the source storage system.

  Therefore, space savings are achieved on the destination storage system.

• If you plan to compress existing data on the disk with the -a or -b option on a source FlexVol volume that has existing qtree SnapMirror relationships, then this might result in a large transfer of data blocks.

  When data compression is complete, all the newly compressed blocks are written as new blocks and all the newly compressed data blocks are transferred in the next incremental transfer.

For more information about qtree SnapMirror, see the Data ONTAP Data Protection Online Backup and Recovery Guide for 7-Mode.