Of hot backup
What is a hot backup ?
Hot backup allows you to back up opened files (files in use by a third party application) without disturbing the system behaviour. For instance, it is possible to perform a hot backup of database files without interrupting their manager and therefore without application downtime. This technology exists on Windows, and the component in charge of this process is called VSS (for Volume Snapshot Services).
Different types of hot backups
There are two types of hot backup and that's where things are getting a bit more complicated.
- The first one is called component mode backup : the application using the data is aware of a current backup and ensures that the files are in a coherent state to the backup software. It is the case for Microsoft SQL Server, Microsoft Hyper-V or Microsoft Exchange.
- The second one is the file mode backup : the application is not aware of the current backup (it was not designed to) and cannot ensure the files' consistency because they are being read while the application still works on them. There are a few exemple like Microsoft Outlook and its
.pstfiles, but also numerous databases not implementing the component mode backup (like Microsoft Access).
What does Arx One Backup do
The backup agent can work using three modes :
- Cold backup, with an usual file opening method. This only works when the file is not already opened by another application.
- Component mode backup, if the file is opened and compatible with this mode (the application itself provides this information).
- Hot backup, if the file is opened and not compatible with the component mode. There is a warning on this specific point : the file is opened and the application does not know the current backup. Therefore, there is a possibility that the file content is not in a coherent state.
How to avoid hot backup in file mode and the associated warning ?
- If the file to back up is part of a database, there are a some options :
- The best option is to stop the database before the backup and to start it again when it is finished. This allows the backup agent to perform a cold backup.
- If the interruption time is too long, you can stop the database, perform a file copy, restart the database and backup the copy result. This method allows to keep the advantage of an efficient data deduplication which are a faster transfer time and a improved disk space usage on the destination.
- If the database cannot be stopped, perform a dump and back it up uncompressed (which will also keep the work simple and efficient for the backup agent).
- If the file is something else than a database, it will need to be considered for each different case. We do not provide miracles yet !