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Data Compression and Deduplication

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To decrease traffic and disk space required for storing backup files, Veeam Backup & Replication provides mechanisms of data compression and deduplication.

Data Compression

Data compression decreases the size of created backups but affects duration of the backup procedure. Veeam Backup & Replication allows you to select one of the following compression levels:

None compression level is recommended if you use storage devices with hardware compression and deduplication tools to store created backups.
Dedupe-friendly is an optimized compression level for very low CPU usage. It is recommended if you want to decrease the proxy load.
Optimal (default setting) is the recommended compression level providing the best ratio between the size of the backup file and time of the backup procedure.
High compression level provides additional 10% compression ratio over Optimal, but at the cost of about 10x higher CPU usage.
Extreme compression provides the smallest size of the backup file but reduces backup performance. We recommend that you run backup proxies on computers with modern multi-core CPUs (6 cores recommended) if you intend to use the extreme compression.


You can apply deduplication when backing up multiple VMs that have similar data blocks (for example, if VMs were created from the same template) or great amount of free space on their logical disks. Veeam Backup & Replication does not store zero byte blocks or space that has been pre-allocated but not used. With deduplication, identical blocks or blocks of free space are eliminated, which decreases the size of the created backup file.

Depending on the type of storage you select as a backup target, Veeam Backup & Replication uses data blocks of different size to process VMs, which optimizes the size of a backup file and job performance. You can choose one of the following storage optimization options:

The Local target (16 TB + backup files) option is recommended for backup jobs that can produce very large full backup files — larger than 16 TB. With this option selected, Veeam Backup & Replication uses data block size of 8192 KB.
If you select to use data blocks of small size to dedupicate a large backup file, the backup file will be cut into a great number of data blocks. As a result, Veeam Backup & Replication will produce a very large deduplication metadata table which can potentially overgrow memory and CPU resources of your backup repository. For backup files over 16 TB, it is recommended to choose the Local target (16 TB + backup size) option. With this option selected, Veeam Backup & Replication will use data blocks of 8 MB. Large data blocks produce a smaller metadata table that requires less memory and CPU resources to process. Note, however, that this storage optimization option will provide the lowest deduplication ratio and the largest size of incremental backup files.
The Local target option is recommended for backup to SAN, DAS or local storage. With this option selected, Veeam Backup & Replication uses data block size of 1024 KB.
The SAN identifies larger blocks of data and therefore can process large amounts of data at a time. This option provides the fastest backup job performance but reduces the deduplication ratio, because with larger data blocks it is less likely to find identical blocks.
The LAN target option is recommended for backup to NAS and onsite backup. With this option selected, Veeam Backup & Replication uses data block size of 512 KB. This option provides a better deduplication ratio and reduces the size of a backup file because of reduced data block sizes.
The WAN target option is recommended if you are planning to use WAN for offsite backup. With this option selected, Veeam Backup & Replication uses data block size of 256 KB. This results in the maximum deduplication ratio and the smallest size of backup files, allowing you to reduce the amount of traffic over the WAN connection.

Changing Data Compression Settings

You can change compression and deduplication settings for existing backup jobs. New settings will not have any effect on previously created backup files in the backup chain. They will be applied to new backup files created after the settings were changed.

To apply new deduplication settings, you must create an active full backup after you change deduplication settings. Veeam Backup & Replication will use the new block size for the active full backup and subsequent backup files in the backup chain.
Compression settings are changed on the fly. You do not need to create a new full backup to use new settings — Veeam Backup & Replication will automatically apply the new compression level to newly created backup files.

However, if you use the reverse incremental backup method, the newly created backup files will contain a mixture of data blocks compressed at different levels. For example, you have a backup job that uses the reverse incremental backup method and the Optimal level of compression. After several job sessions, you change the compression level to High. In the reverse incremental backup chains, the full backup file is rebuilt with every job session to include new data blocks. As a result, the full backup file will contain a mixture of data blocks: data blocks compressed at the Optimal level and data blocks compressed at the High level.

If you want the newly created backup file to contain data blocks compressed at one level, you can create an active full backup. Veeam Backup & Replication will retrieve data for the whole VM image from the production infrastructure and compress it at the new compression level. All subsequent backup files in the backup chain will also use the new compression level.

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