The Windows Volume Shadow Copy Service (VSS), available on several Windows operating systems, provides the ability to create snapshots, or point-in-time (PIT) copies, of shares and volumes. These snapshots are images of the data on the disk as it looks at a particular point in time. By keeping these images of data, you can quickly recover individual files or entire volumes directly from the disk as they appeared when the snapshot was taken.
It is important to be aware that when VSS is enabled on a volume with a cluster size smaller than 16 KB, VSS will see file movement done by the defragmentation process as "changed data" and take a point-in-time snapshot, even though only the location of the data has changed. Unnecessary snapshots will cause the VSS storage area to increases in size, possibly resulting in earlier VSS snapshots being purged. Diskeeper provides special defragmentation methods to allow you to defragment these VSS enabled volumes, yet minimize the possibility that older VSS snapshots will be purged.
When the VSS defragmentation option is enabled, Diskeeper uses proprietary defragmentation engines to help reduce the chance of the defragmentation operation causing new VSS snapshots from being created, thus potentially preventing older snapshots from being purged. In order to do this, the VSS defragmentation engines use more conservative file movement algorithms, which can result in slightly less thorough defragmentation of the volume. Despite this, performance is still improved when this method is enabled. (Keep in mind that a large file in two pieces has virtually no performance loss, but it shows as much red color in the Volume Map as a file in several thousand pieces, which does suffer from performance loss.)
The VSS defragmentation method is not enabled by default on VSS enabled volumes, but you can change this default for both Automatic and Manual defragmentation operations via the Volume Shadow Copy Service (VSS) Options.
There are several options available to control how Diskeeper handles VSS enabled volumes.
These options are available via the Volume Shadow Copy Service (VSS) Options area of the System tab in the Advanced Configuration Settings screen.
Note: These options will only affect VSS enabled volumes with a cluster size smaller than 16 KB.
Diskeeper provides these options for Automatic Defragmentation of VSS enabled volumes:
Defragment using VSS defragmentation method
Select this option to use special Automatic Defragmentation engines optimized for VSS enabled volumes. This option minimizes growth of the VSS storage area caused by file movement and reduces the chance of older VSS snapshots being purged.
Defragment using standard defragmentation method
Select this option to use the standard Automatic Defragmentation engines on VSS enabled volumes. Be aware that enabling this option can increase the size of the VSS storage area and can result in some or all of the VSS snapshots being purged.
Do not defragment VSS volumes
Select this option to prevent Automatic Defragmentation from running on any VSS enabled volumes.
Diskeeper provides these options for Manual Defragmentation of VSS enabled volumes:
Defragment using VSS defragmentation method
Select this option to use special Manual Defragmentation engines optimized for VSS enabled volumes. This option minimizes growth of the VSS storage area caused by file movement and reduces the chance of older VSS snapshots being purged.
Defragment using standard defragmentation method
Select this option to use the standard Manual Defragmentation engines on VSS enabled volumes. Be aware that enabling this option can increase the size of the VSS storage area and can result in some or all of the VSS snapshots being purged.