254 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
If a signature match is found, the data chunk is replaced by a reference to a stored chunk, 
which reduces storage space that is required for storing the data. Conversely, if no match is 
found, the data chunk is stored without modification and its signature is added to the 
deduplication database. 
To maximize the space that is available for the deduplication database, the system distributes 
it between all nodes in the I/O groups that contain deduplicated volumes. Each node holds 
a distinct portion of the records that are stored in the database. If nodes are removed or 
added to the system, the database is redistributed between the anodes to ensure optimal use 
of available resources. 
Depending on the data type that is stored on the volume, the capacity savings can be 
significant. Examples of use cases that typically benefit from deduplication are virtual 
environments with multiple VMs running the same operating system and backup servers. In 
both cases, it is expected, that multiple copies of identical files exist, such as components of 
the standard operating system or applications that are used in the organization. Conversely, 
data that is encrypted or compressed at the file system level do not benefit from deduplication 
because these operations remove redundancy of the data patterns. 
Although deduplication (as with other features of IBM Spectrum Virtualize) is transparent to 
users and applications, it needs to be planned for and understood before implementation 
because it might reduce the redundancy of a solution. For example, if an application stores 
two copies of a file to reduce chances of data corruption by way of a random event, the copies 
are deduplicated and thus the intended redundancy is removed from the system if these 
copies are on the same volume.
When planning the use of deduplicated volumes be aware of update and performance 
considerations and the following software and hardware requirements:
/SM590000Code level V8.1.2 or higher is needed for data reduction pools.
/SM590000Code level V8.1.3 or higher is needed for deduplication.
/SM590000Nodes must have at least 32 GB memory to support deduplication. Nodes that have more 
than 64 GB memory can use a bigger deduplication fingerprint database, which might lead 
to better deduplication.
/SM590000You must run supported IBM Storwize V7000 hardware. For more information about the 
current table that specifies valid hardware and features combinations, see this website. 
7.1.11  Capacity reclamation
File deletion in modern file systems is realized by updating file system metadata and marking 
the physical storage space that is used by the removed file as unused. The data of the 
removed file is not overwritten. This improves file system performance by reducing the 
number of I/O operations on physical storage required to perform file deletion. 
However, this approach affects the management of real capacity of volumes with enabled 
capacity savings. File system deletion frees space at the file system level, but physical data 
blocks that are allocated by the storage for the file still take up the real capacity of a volume. 
Note: You can use the management GUI or the command-line interface to run the built-in 
compression estimation tool. This tool can be used to determine the capacity savings that 
are possible for existing data on the system by using compression.