Home > Storage > PowerMax and VMAX > Storage Admin > Dell PowerMax: Data Reduction > Local replication (SnapVX)
Data reduction is supported with the use of local replication features; there are multiple variations and use cases for local replication. Below are the details regarding the different local replication sessions that can exist. For more detail regarding local replication and SnapVX see the TimeFinder and HYPERMAX OS Local Replication Technical Note available at DellEMC.com.
Uncompressed source data remains uncompressed when becoming snapshot data and may be compressed later as it becomes less active. Activity to snapshot data through a linked target may prevent uncompressed data from being compressed. Compressed source data remains compressed when becoming snapshot data. Read activity to a snapshot through a linked target may cause the compressed data to be uncompressed.
The compression setting of a linked target only affects data written directly to the linked target and does not affect the snapshot data.
The compression settings for both the source and target are taken into account for copy sessions.
When compression is enabled on the source the data is decompressed before copying to the target. When compression is enabled on the target the data is compressed before being allocated to the target. Likewise, when compression is enabled on both the source and target the data is decompressed before the copy and then compressed to allocate for the target.
Copy times may vary due to decompression and compression of the data. It is not recommended to change the compression settings in between differential operations (that is, disabling compression before each differential operation and then again after the copy completes) as this causes data to go through needless compress/decompress cycles.