EMC DL3D 1500, Administrator'S Manual

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Data reduction 21
About the DL3D 1500/3000
de-duplication lets you select either scheduled or immediate
techniques. Data storage is available in both virtual tape library
(VTL) and network attached storage (NAS) formats.
Data reduction
Data reduction is the process of reducing the amount of storage
capacity required to store data. The DL3D 1500/3000 appliances
provide two techniques to optimize the storage space required on
your system:
◆
Data de-duplication
◆
Hardware compression
Data de-duplication
The DL3D 1500/3000 appliance can reduce the amount of storage
capacity required by using data de-duplication. The DL3D series disk
backup and replication systems use data de-duplication technology
to increase the role that disks can play in data protection. This
advantage lets IT departments cost-effectively retain months of
backup data on disk for faster, more reliable restores and more data
recovery points. The DL3D 1500/3000 supports immediate and
scheduled de-duplication policies (as well as no de-duplication) on
individual shares or VTLs.
◆
Immediate de-duplication - As the DL3D appliance ingests the
backup data, the DL3D writes the data to disk in its native format.
The de-duplication process is initiated when the first 256 MB of
data is received and continues during data ingest.
◆
Scheduled de-duplication - This policy allows you to specify a
time window during which de-duplication will not occur.
Typically, this time window is the backup window. It allows the
backup to be ingested at maximum rates for time critical backup
windows. De-duplication begins on the data (already present in
native format on disk) as soon as the schedule window expires.
The de-duplication process divides the backup data into variable
length blocks and creates a signature for each block. For each
signature, the de-duplication process determines if any other
identical signature already exists, and if not, it compresses the unique
block and writes it to its data pool. If it finds any matches to these
signatures, it replaces that redundant block with a pointer to the