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The deduplicated items that have changed are not identical anymore and therefore will not be
deduplicated.
2.12.6.4
Deduplication best practices
Follow these recommendations when using deduplication:
When creating a deduplicating vault,
place the vault and its deduplication database on different
disks.
This will make deduplication faster, because deduplication involves extensive simultaneous
use of both the vault and the database.
Indexing of a backup requires that the vault have
free space with a minimum size of 1.1
multiplied by the size of the archive the backup belongs to
. If there is not enough free space in
the vault, the indexing task will fail and start again after 5–10 minutes, on the assumption that
some space has been freed up as a result of cleanup or of other indexing tasks. The more free
space there is in the vault, the faster your archives will reduce to the minimum possible size.
When backing up multiple systems with similar content,
back up one of the similar systems first,
so that Acronis Backup & Recovery 10 Storage Node indexes all the system's files as potential
deduplication items. This will lead to faster backup processes and less network traffic (because of
effective deduplication at source), regardless of whether the backups are performed
simultaneously or not.
Before starting the subsequent backups, make sure that the
indexing task has finished
deduplication of the first backup and is now idle. You can view the state of the indexing task in
the list of tasks on Acronis Backup & Recovery 10 Management Server.
2.12.6.5
Deduplication ratio
The deduplication ratio shows the size of archives in a deduplicating vault in relation to the size they
would occupy in a non-deduplicating vault.
For example, suppose that you are backing up two files with identical content from two machines. If
the size of each file is one gigabyte, then the size of the backups in a non-deduplicating vault will be
approximately 2 GB, but this size will be just about 1 GB in a deduplicating vault. This gives a
deduplication ratio of 2:1, or 50%.
Conversely, if the two files had different content, the backup sizes in non-deduplicating and
duplicating vaults would be the same (2 GB), and the deduplication ratio would be 1:1, or 100%.
What ratio to expect
Although, in some situations, the deduplication ratio may be very high (in the previous example,
increasing the number of machines would lead to ratios of 3:1, 4:1, etc.), a reasonable expectation
for a typical environment is a ratio between 1.2:1 and 1.6:1.
As a more realistic example, suppose that you are performing a file-level or disk-level backup of two
machines with similar disks. On each machine, the files common to all the machines occupy 50% of
disk space (say, 1 GB); the files that are specific to each machine occupy the other 50% (another
1 GB).
In a deduplicating vault, the size of the first machine's backup in this case will be 2 GB, and that of
the second machine will be 1 GB. In a non-deduplicating vault, the backups would occupy 4 GB in
total. As a result, the deduplication ratio is 4:3, or about 1.33:1.
