Dell Storage Manager 2020 R1 Administrator's Guide

PDF

About Data Reduction

The FluidFS cluster supports two types of data reduction:

Data deduplication – Uses algorithms to eliminate redundant data, leaving only one copy of the data to be stored. The FluidFS cluster uses variable-size block level deduplication as opposed to file level deduplication or fixed-size block level deduplication.
Data compression – Uses algorithms to reduce the size of stored data.

When using data reduction, note the following limitations:

The minimum file size to be considered for data reduction processing is 65 KB.
Because quotas are based on logical rather than physical space consumption, data reduction does not affect quota calculations.
If you disable data reduction, data remains in its reduced state during subsequent read operations by default. You can enable rehydrate-on-read when disabling data reduction, which causes a rehydration (the reversal of data reduction) of data on subsequent read operations. You cannot rehydrate an entire NAS volume in the background, although you could accomplish this task by reading the entire NAS volume.
Cross-volume deduplication is not supported at this time.
Data reduction does not support base clone and cloned volumes.

Table 1. Data Reduction Enhancements in FluidFS v6.0 or later
FluidFS v6.0 or later	FluidFS v5.0 or earlier
Data reduction is enabled on a per-NAS-cluster basis.	Data reduction is enabled on a per-NAS-volume basis.
Data reduction supports deduplication of files that are created or reside on different domains.	Data reduction is applied per NAS controller, that is, the same chunks of data that are owned by the different NAS controllers are not considered duplicates.
The distributed dictionary service detects when it reaches almost full capacity and doubles in size (depending on available system storage).	The dictionary size is static and limits the amount of unique data referenced by the optimization engine.