Backup and Restore
Logging and recovery also play a role in protecting data from media failure. ESE supports on-line backup where one or more databases are copied, along with log files in a manner that does not affect database operations. Databases can continue to be queried and updated while the backup is being made. The backup is referred to as a ‘fuzzy backup’ because the recovery process must be run as part of backup restoration to restore a consistent set of databases. Both streaming and shadow copy backup are supported.
Streaming backup is a backup method where copies of all desired database files and the necessary log files are made during the backup process. File copies may be saved directly to tape or can be made to any other storage device. No quiescing of activity of any kind is required with streamed backups. Both the database and log files are check summed to ensure that no data corruptions exist within the data set during the backup process. Streaming backups may also be incremental backups. Incremental backups are ones in which only the log files are copied and which can be restored along with a previous full backup to bring all databases to a recent state.
Shadow copy backups are a new high speed backup method. Shadow copy backups are dramatically faster because the copy is virtually made after a brief period of quiescing an application. As subsequent updates are made to the data, the virtual copy is materialized. In some cases, hardware support for shadow copy backups means that actually saving the virtual copies is unnecessary. Shadow copy backups are always full backups.
Restore can be used to apply a single backup, or it can be used to apply a combination of a single full backup with one or more incremental backups. Further, any existing log files can be replayed as well to recreate an entire data set all the way up to the last transaction logged as committed to transaction level 0. Restoration of a backup can be made to any system capable of supporting the original application. It need not be the same machine, or even the same machine configuration. Location of files can be changed as part of the restoration process.
Read more about this topic: Extensible Storage Engine
Famous quotes containing the word restore:
“We often have need of a profound philosophy to restore to our feelings their original state of innocence, to find our way out of the rubble of things alien to us, to begin to feel for ourselves and to speak ourselves, and I might almost say to exist ourselves.”
—G.C. (Georg Christoph)