At start of backup, a Snapshot is taken of all disks to be backed up. The Snapshot is then backed up. This has the advantage, that the state of all backed up files is taken at the same time. Stratesave also backs up the System State "VSS-aware", following the VSS guidelines.
VSS Writers can be selected for backup under VSS-database tree. For example Hyper-V, Exchange Server, SQL Server have writers and are therefore selectable under VSS. SQL Server databases are selectable under Service State\MSDEWriter. If the SQL Writer Service is running, SQL Server databases are under VSS\SqlServerWriter. Backups of VSS databases are full backups, and differential backups if the VSS-writer supports that. For example, VSS Exchange Server supports incremental backups, but not SQL Server.
SQL Server VSS full backups can be combined with normal differential and incremental SQL Server backups.
While VSS databases are backed up as files it is not sufficient to select for backup only the directories where databases are stored. Only if the databases are selected under VSS tree there is the correct snapshot which is created in cooperation with the writers. If the VSS databases and the corresponding files/directories are both selected, there is no duplication in backup, each VSS database internally points to its database file(s). So it is possible to select entire drives and the VSS databases.
During Disaster Recovery, where in the first step the partition images are restored or all files and directories with System State, it is often not necessary to do the second restore step for the VSS databases, because the database data is already restored with the files and the configuration is also restored with files and registry.
To build and maintain a Snaphot, backup privilege is required and enough free disk space must be available. If not enough disk is available, Snapshot automatically terminates during backup, and backup fails on error, or directory will be skipped.