Acronis Backup for Windows Server Essentials - User Guide - Manual (Page 221)

221 Copyright © Acronis International GmbH, 2002-2014
Every time the compacting task starts, the storage node determines whether to perform compacting.
To do this, the storage node:
1. Checks the size of the backed-up data that has been deleted from the vault since the last
compacting.
2. Uses the Compacting Trigger Rough Estimation Threshold parameter to determine whether this
size, relative to the size of the remaining backed up data, is significant.
3. If so, uses the Compacting Trigger Threshold parameter to determine whether the deduplication
data store contains a significant number of unused items. If so, the storage node performs
compacting.
The parameters are the following.
Compacting Trigger Rough Estimation Threshold
Description: Specifies the relative size of the backed-up data that remains in a deduplicating vault,
below which checking for unused items is performed (see the Compacting Trigger Threshold
parameter).
Possible values: Any integer number between 0 and 100
Default value: 90
The Compacting Trigger Rough Estimation Threshold parameter enables you to skip the check
for unused items (and hence skip compacting) when the content of the vault did not change
significantly.
The larger the value of this parameter, the more often the check for unused items will be
performed. The value 100 means that the check will be performed each time the compacting
task starts.
How it works. Assume that the parameter value is 90 and the vault has 100 GB of backed up data.
It does not matter whether this data has duplicates. Then, you delete a few backups and the
backed-up data size becomes equal to 80 GB. In this case:
The size of the deleted data is 20 GB, and the size of the remaining data is 80 GB. The ratio of the
deleted to remaining data is thus 20 GB / 80 GB = 0.25, or 25 percent.
The storage node calculates the relative size of the remaining data as 100 percent – 25 percent =
75 percent.
Because this relative size is less than 90 percent, the storage node starts checking for unused
items.
Compacting Trigger Threshold
Description: Specifies the percentage of used items in the deduplication data store below which
compacting occurs.
Possible values: Any integer number between 0 and 100
Default value: 90
Since compacting is a resource-consuming operation, it should occur only when the number of
unused items is significant.
The Compacting Trigger Threshold parameter enables you to set up a balance between the extra
space required to store unused items and the compacting frequency. The larger the value of this
parameter, the fewer unused items are allowed in the data store, but compacting will likely be
more frequent.
The check is performed only after checking the percentage of the remaining backed up data in
the vault (see the Compacting Trigger Rough Estimation Threshold).