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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:
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.
See Enable or Disable Hardware Compression for step-by-step instructions.
Note the following for using Hardware Data Compression for data protection operations involving the NAS iDataAgents:
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.
Software compressed data is not uncompressed during an auxiliary copy operation.
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.
See Enable Decompress Data before Backup for a NetWare File System Backup Set for step by step instructions.
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.
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