When should “Enable VSS support” option be enabled in Backup > Schedule Volumes or Backup > Schedule Folder page?
Shadow Copy is a is a technology included in Microsoft Windows that allows taking manual or automatic backup copies or snapshots of data, even if it has a lock, on a specific volume at a specific point in time over regular intervals. It is implemented as a Windows service called the Volume Shadow Copy service (VSS).
Snapshots have two primary purposes: -
1) allow the creation of consistent backups of a volume, ensuring that the contents cannot change while the backup is being made; and they avoid problems with file locking
2) by creating a read-only copy of the volume, backup programs are able to access every file without interfering with other programs writing to those same files.
Applications can provide specific support for VSS through VSS writers which control how data is set to a consistent state at the beginning of a VSS operation and maintain that consistency throughout the process, among other functions. Windows applications and services that support VSS include Hyper-V, Virtual Server,Active Directory, SQL Server, Exchange Server, SharePoint and some third-party solutions such as Oracle.
Kaseya Backup (Acronis) VSS implementation
Older versions of Acronis software had an Acronis proprietary VSS provider which was unreliable in some environments. Kaseya Backup v3.2 and above use Windows native VSS provider on clients with an Acronis build that supports it (Acronis v9.7 and above).
When to use VSS option
VSS should be enabled if: -
1) you need to ensure a VSS compliant application such as those listed above are backed up in a clean and consistent state. If you are not sure whether an application is VSS compliant, contact the software vendor.
2) you are taking a folder based backup of files which may be in use or locked at the time of the backup
Do VSS backups take applications or databases offline?
No, but applications that have VSS writers will freeze write I/O requests for a maximum of 60 seconds during snapshot creation process. This may affect performance if the backup is taken at a busy time.
Can I restore a database from a non-VSS backup?
Yes, but it may have been backed up in a “crash consistent” state with incomplete I/O operations or data corruption. Some additional steps may be needed to recover to a usable state.
Are database transaction logs flushed to disk?
How a database is prepared for VSS snapshot is the responsibility of the application’s VSS writer. Contact the application vendor for details.
A detailed description of the VSS process can be found here - http://technet.microsoft.com/en-us/library/cc757854(WS.10).aspx
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