Dell EqualLogic PS6210XS EqualLogic Group Manager Administrator s Guide PS Ser - Page 212

The data reduction settings are shown at the bottom of the status information panel. NAS Container Data Reduction Data reduction is a process that runs according to a schedule on each NAS container that has data reduction enabled. A policy that you define determines whether or not a file qualifies for data reduction, on the basis of access and modification times of that file. The data reduction process analyzes files to determine if multiple copies of an individual file, or portions of a file, or blocks, can be saved in a more efficient format. The PS Series controller manages the data reduction schedule, which defines when the data reduction process begins and ends, and how frequently data reduction is performed. The NAS array controller manages the data reduction process. NOTE: To configure and enable the data reduction feature on a NAS container, you must have group administrator (grpadmin) privileges. User quotas are enforced based on logical data size, not on the physical footprint of the data. If two users each have a copy of the same 1GB file, the physical footprint of the file is 1GB after data reduction, and both users use 1GB of their individual user quota. If data reduction is disabled, the user quota will continue to be enforced based on the logical space utilization until all the reduced data is rehydrated. Data reduction occurs: • During the time and days specified in a schedule. • When a file has not been accessed or modified for the duration of time defined by the file filters in the data reduction policy. NOTE: Enabling data reduction on a container permanently removes the snapshot reserve functionality for that container. Snapshot reserves cannot be enabled even if you later disable data reduction. Snapshots can still be manually created, deleted, and restored, and automatically deleted when the maximum number of snapshots to keep is exceeded. Data reduction is accomplished through two methods: • Deduplication - Applied whenever data reduction is enabled. Deduplication replaces qualified duplicated data with a pointer to a single copy of the data. • Compression - Applied only when compression is enabled as part of the data reduction policy. Compression occurs within files when individual blocks can be saved in a more efficient format than originally written. Data reduction is performed on blocks in 128KB chunks. Space savings from data reduction are reported in MB units. Deleting a reduced file will not result in additional free disk space on the container, unless the file being deleted is the last copy of that file. Free space gained from deleting the last copy of a file will not be available until the disk cleaner process cleans the file marked for deletion. When you enable data reduction on a NAS container, default data reduction policy settings are applied to that container. You can modify the default policy settings or define other policy settings. The data reduction policy specifies if data compression is applied and determines if files qualify for data reduction based on the last time they were accessed and modified. For more information about setting default values, see Creating Default Data Reduction Properties of a NAS Cluster. Data reduction affects system performance. When a reduced file is accessed, the controller reads a copy of the deduplicated data and uncompresses the data as it is being sent to a client. Unless the reduced data is modified, it remains reduced on the disk. After data reduction is disabled, if at least 5GB of free space is available on the container, when data is read on the container, the data is uncompressed. When deciding whether or not to enable data reduction, consider the storage resource and data reduction processing efficiency of your system. 212 NAS Container Operations