Compression; Space Reclamation - Quantum DXi4500 User Manual

Chapter 1: DXi4500 System Description

Space Reclamation

Compression

Space Reclamation
4
than with conventional arrays. This advantage allows IT departments to
cost-effectively retain months of backup data on disk for faster, more
reliable restores and more data recovery points. Quantum's innovative
implementation of this core technology means that users do not have to
compromise on performance to take advantage of extended retention
capability. DXi solutions support both in-line and post-processing data
deduplication methodologies—allowing users to realize optimal use of
disk resources and achieve the performance needed to complete critical
jobs during short backup windows.
The DXi4500 system can reduce the amount of storage capacity
required through a data deduplication process. The term data
deduplication refers to the elimination of redundant data. Data
deduplication works by recognizing repeated variable-length blocks of
data in a stream of data. Only a single instance of each blocklet is stored
and references (tags) are made for all of the duplicate variable-length
blocks of data. These references or tags are stored in an index for use
later to reconstitute the deduplicated data. By only storing one instance
of the blocklet, a great deal of capacity is saved. For a NAS share, the
DXi system waits for 60 seconds of inactivity before a file can be
deduplicated. For more information on enabling data deduplication, see
NAS Configuration on page 54.
The DXi4500 systems use compression technology after duplicate blocks
have been identified and replaced as part of the deduplication process.
With compression, unique data that has been through the data
deduplication process can be compressed at a typical ratio of
approximately 2:1. This enables you to maximize the storage capacity of
your system.
The space reclamation process performs multiple functions on the
DXi4500.
When data is deduplicated it is stored in what we refer to as a block
pool—a pool of all unique data blocks that were captured during the
data deduplication cycle. When subsequent backup jobs occur, the data
Quantum DXi4500 User's Guide