PowerFlex 3.X: Compression Ratio (Maximum, Theoretical) and Oversubscription

Max compression ratio is an attribute of a fine-granularity storage pool in PowerFlex 3.x, its default value is 10.
 

 [root@node1 ~]# scli --query_all
<<SNIP>> Storage Pool SP-1 (Id: xxxxxxxxxxxxxxxx) has 1 volumes and 8.6 TB (8851 GB) free net capacity. 172.9 TB (177016 GB) volume allocation limit.         The number of parallel rebuild/rebalance jobs: 2          <<SNIP>>         Fine granularity advanced configuration:                    <<SNIP>>                 NVDIMM metadata amortization 1.50                 Max compression ratio: 10                 Performance profile: high_performance <<SNIP>> 

Whereas theoretically the compression ratio of PowerFlex 3.x can be up to 64:1.
For Example: 31.6:1 from a UI snapshot below

 

Symptom

The "compression ratio" is higher than "Max compression ratio."

Explanation

The Max compression ratio is a limit on how much user data can be stored in the entire storage pool.

maximum_user_data = storage_pool_raw_capacity * max_compression_ratio

The "compression ratio" on the other hand, is a ratio of the currently stored user data over the used physical capacity. This depends on the compressibility of the user data under the compressing algorithm employed.