When backing up a file that is being written, it is impossible to guarantee integrity of a backup copy of that file. This is typical for backing up frequently accessed databases, email systems, etc. To handle these scenarios, Microsoft Windows uses the Volume Snapshot Service (VSS) technology that lets the users to take backup copies of files or volumes, even when they are in use. VSS first creates a snapshot of the volume to back up. A snapshot is a read-only copy of the volume taken at certain point in time. VSS ensures that the contents to back up do not change and are not locked while the backup is being performed.
Linux does not provide similar technology, so we have developed our own snapshot technology called CloudBerry Snapshot Driver for Linux (or Snaphot driver in this document).
The Snapshot Driver for Linux is a part of upcoming CloudBerry Linux Image Based Backup designed to ensure data integrity while performing Image Based backup operations.
How It Works
Our technology involves two interrelated things: snapshot device and snapshot driver. The snapshot device is a mirror of the selected disk partition. If an application tries to modify a file that belongs to the selected disk partition, the snapshot driver automatically copies the parts of the file being read to the snapshot device. The application can then overwrite the data on the disk, while the snapshot device contains the original data. Thus, the snapshot device contains the state of all original files as they were when the snapshot was created.