Data compression options are provided for data secured by data protection operations. Compression
reduces the quantity of data sent to storage, often doubling the effective
capacity of the media (depending on the nature of the data). If the data is
later restored/recovered, the system automatically decompresses the data and restores
it to its original state.
The following data compression options are provided:
Software compression which includes options to compress the data in the:
Client
MediaAgent
Hardware compression for libraries with tape media at the individual
data path
As compressed data often increases in size if it is again subjected to
compression, the system only applies one type of compression for a given
data protection operation. You can redefine the compression type at any time without compromising
your ability to restore/recover data.
When hardware compression is available and applied, it has precedence over
the other compression selections. If hardware compression is enabled for a data
path, then all data conducted through that data path is compressed using the
hardware compression. If
hardware compression is disabled for a data path, then the data is handled in
accordance with the software compression selection of each subclient that backs
up to the data path. Selections under each subclient include options for Client compression, MediaAgent compression,
or no compression.
Also keep in mind that hardware compression is not applicable for disk
libraries and hence the software compression selection for subclient is used for
data paths associated with disk libraries.
Note that at any given time you can view the compression scheme used for
protecting a subclient's data by viewing the details of the data paths
associated with the subclient. See
View Data Paths Associated
With a Subclient for step-by-step instructions.
The client compression is specified on the subclient level for most
agents. (For database iDataAgents, this
is specified on the instance level.)
Client compression is available for all storage media. This scheme compresses
the data on the client computer using the compression software. The compressed data
is then sent to the MediaAgent which in turn directs it to a storage media. Client compression
is useful if the client and MediaAgent reside on separate computers and
therefore the client must send its data using a network. Client compression
reduces the network load since the data is compressed before it leaves
the client.
Note that client compression may not be suitable in all circumstances. Using
software to compress data can be processor intensive. Consequently, you may not
want to use client compression for client systems with limited processing power.
In such cases, MediaAgent compression may be more efficient.
The diagram on the right illustrates Client Compression.
For the Quick Recovery Agent, when the client compression is enabled, objects
are compressed on the source computer in the beginning of the copy and
uncompressed on the destination computer at the end of the copy.
Data being replicated can be compressed between the source and destination
computers. When compression is enabled, data is compressed on the source
computer, replicated across the network to the destination computer, and
uncompressed on the destination computer, thereby reducing the network load. Compression for replication is specified on the Replication Set level, and
applies to all of its Replication Pairs. For a given Replication Set, you can enable or disable client compression
between the source and destination machines. See
Enable or Disable Software Compression for a Replication Set for
step-by-step configuration instructions.
The diagram on the right illustrates Replication Compression.
The MediaAgent compression is specified on the subclient level for most
agents. (For database iDataAgents
like SAP for Oracle, Oracle, etc. the compression type is specified on the instance level). For a
given subclient or instance as appropriate, you can enable or disable MediaAgent compression for all data
paths which do not have hardware compression enabled.
MediaAgent compression is available for all storage media. This scheme
compresses the data on the MediaAgent using compression software in the
MediaAgent. The compressed
data is then sent from the MediaAgent to the storage media. MediaAgent
compression can be useful if the MediaAgent software resides on a computer that
is more powerful than the client computer. Using software to compress data can
be processor intensive; consequently, you may want to use MediaAgent compression
for client computers with limited processing power.
The diagram on the right illustrates MediaAgent Compression.
Note that data compressed on the MediaAgent during data protection, is decompressed on the client
computer during the data recovery.
See the following procedures for step-by-step instructions on enabling (or
disabling) software compression:
The hardware compression is established on the data path level. This
kind of compression is only available for data paths that direct data to
tape libraries. This compression scheme sends uncompressed data from the
client computer through the data path to the media. There the
tape drive hardware compresses the data before writing it to the media.
Generally, hardware compression is faster than software compression since it
is performed by dedicated circuitry. This compression scheme is particularly
suited for direct-connect configurations where the subclient and MediaAgent are
hosted by the same physical computer. In such configurations, there are no
network bottlenecks that can throttle the transfer of data to the media drives.
Therefore, the drives can compress the data as quickly as it is sent by the
subclient. In such configurations, hardware compression can not only boost the
virtual capacity of the tape but the performance of the data protection
operation as well, because the
tape, operating at high speed, stores more data per unit time than it would
otherwise.
The diagram on the right illustrates Hardware Compression.
Note that hardware compression is only supported by tape libraries. Hardware
compression is not applicable for disk and optical libraries.
Hardware compression may be less useful when data secured by data protection operations
must compete with
other data for network bandwidth. If the network becomes congested, the tape
drives can become starved for data. In this condition, the drives still compress
the data, but because data is not supplied quickly enough, the drives must stop
and restart the media as more data becomes available. As a result, performance
may suffer.
Note the following for using Hardware Data Compression for data protection
operations involving the NAS iDataAgents:
For a tape drive attached to a NetApp file server, hardware compression
is always on.
For a tape drive attached to a BlueArc or EMC Celerra file server,
hardware compression can be configured in the normal manner.
For any of the NAS iDataAgents, when using NDMP Remote Server (NRS)
and a drive pool configured to a MediaAgent, hardware compression can be
configured in the normal manner.
When deduplication storage policy is configured, compression is
automatically enabled on the storage policy copy. All subclients
associated to the deduplication storage policy will use the compression
settings set on the storage policy copy. When the subclient is
associated to deduplicated storage policy, by default Use Storage
Policy Settings option is enabled at subclient level.
For non-deduplicated storage policy, the compression settings need to
be configured on the subclient level and depending upon your environment
select On Client or On MediaAgent compression options.
The NetWare File System data can be in compressed format on a volume that
supports compression, and data in compressed format can only be restored to a
volume that supports compression. The Decompress Data before Backup option
allows you to select whether to decompress data that is in compressed format on
the backup media and can be restored to either a compressed or uncompressed
volume. By default, data is backed up in a compressed format if the data is on a
volume that supports compression.
Software Compression is made part of subclient policy. Once the subclient policy is associated to a backup set, software compression can be overridden at subclient, if necessary.
While configuring the Windows File System backup sets, if you are using
Data Classification as the scan method, you may face the following data
compression issue: When the data is restored, a non-compressed file, in a
compressed folder, becomes compressed.
This issue does not occur if you use the Change Journal or Classic Scan as the
scan method during the backup.
