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Generating A Backup Set

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A backup set is a list of all files to be backed up, their locations, and how to back them up.

A requester must make use of the files contained on the shadow-copied volumes after the IVssBackupComponents::DoSnapshotSet returns successfully to generate the full list of files to be backed up.

In addition, a requester must deal with the possibility that some files have alternate paths and that some files have been excluded.

An algorithm for selecting files to back up should go on a writer instance by writer instance, component-by-component basis (as will be the case during restore; see Generating a Restore Set) and might proceed by doing the following:

  1. Determining the volumes that contain the writer's files and the corresponding device objects
  2. Using the file set information (contained in IVssWMFiledesc objects returned by IVssExamineWriterMetadata::GetExcludeFile) to create a list of the explicitly excluded files, if necessary using FindFileFirst, FindFileFirstEx, and FindNextFile.
  3. Iterating over all of a writer's components, using IVssExamineWriterMetadata::GetComponent. If a selectable component is selected, use logical path to obtain those nonselectable components associated with it in a component set. (See Working with Selectability and Logical Paths.)
  4. Obtaining the file sets contained in each selected component by using the IVssWMComponent interface corresponding to each component it contains.
  5. Generating a list of files from the specifications—if necessary using FindFileFirst, FindFileFirstEx, and FindNextFile.
  6. Checking each file in the list generated from component information against the list of excluded files generated above. This should be done using the default path for the file (returned by IVssWMFiledesc::GetPath), not by the alternate path returned by IVssWMFiledesc::GetAlternateLocation). If the file matches the excluded list, it will not be backed up.
  7. Choosing the actual location from which to back up (using the alternate path if it was set)
  8. At this point, a full list of files and their locations is available and a backup can begin.

After an initial backup set has been generated for all writers that are present on the system, the requester then checks the following registry key:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\BackupRestore\FilesNotToBackup

The requester uses the subkeys under this key as follows:

  • If a writer is present on the system, and there is a subkey whose name matches the writer's name, that subkey must be ignored.
  • If a writer was present on the system but is currently absent from the backup set, and there is a matching subkey, any files specified in the subkey data are excluded and must be removed from the backup set.
  • The backup application adds files to the subkey data by creating a MULTI_SZ value containing a list of file specifications for the files that must not be backed up. Each string in the MULTI_SZ value should contain one file specification.
  • File specifications can contain the ? and * wildcard characters. A specification can be made recursive by appending /s to the end. For example, specifying "%TEMP%\* /s" causes all files in the %TEMP% directory and all of its subdirectories not to be backed up.