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About Hot Backup

What is Hot Backup?​

Hot backup allows open files (i.e., files currently being used by a third-party application) to be backed up without interrupting system operation.
This means that database files can be backed up while they are in use, without stopping the database and without interrupting the system.

This technique exists on Windows, and the component orchestrating hot file access is called VSS (Volume Snapshot Services).

Different Types of Hot Backup​

Things become more complex because there are two types of hot backup:

  • The first is component mode backup: the application is aware that a backup is in progress and ensures that the files provided to the backup system are in a consistent state. This is the case for Microsoft SQL Server, Microsoft Hyper-V, and Microsoft Exchange.
  • The second is file mode backup: the application is not aware that a backup is taking place (because it was not designed for it), so no guarantee can be given regarding file consistency. The file is read while the application is working on it. Examples include Microsoft Outlook .pst files and some databases that do not implement component-level backup (such as Microsoft Access).

What the Arx One Backup Agent Does​

The backup agent can operate in three modes:

  1. Cold backup, meaning an attempt to open the file normally. This works if the file is not opened by another application.
  2. Component mode backup, if the file is open and compatible with this mode (the application provides this information).
  3. Hot backup, if the file is open and not compatible with component mode. This is where a warning is generated: since the file is opened without notifying the application that is using it, it may be in an inconsistent state.

How to Avoid File-Mode Hot Backup and Its Warning​

  • If the file is a database file, several options are available:
    • The best option is to stop the database before the backup and restart it afterward, so the backup agent can access the files in cold mode.
    • If downtime is not acceptable, stop the database, copy the database files, restart the database, and back up the copy. This helps maintain effective deduplication and reduces transfer time and storage usage.
    • If the database cannot be stopped, perform a dump and back up the uncompressed dump (this also makes the backup agent’s work easier).
  • For other types of files, each case must be handled individually; unfortunately, there is no universal solution.