Question

Back-up, VSS, Restore Point, LKG, rollback features and characteristics

Answer 1

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Here we are disussing about data storage, backup and recovery.

Data stores either in primary memory such as main memory, cache memory or in secondary memory such as flash memory, hard disk, magnetic tapes etc.

In certain cases the storage area where we store our data may crashes which leads to loss our data. There is the importance of data backup.

Normally if the data is storing in primary memory, the data backup in secondary memory can recover if the primary memory crashes, But if the secondary memory itself crashes there are some methods to recover the data.

Remote Backup: If we backup our data in remote network storage locations, we can periodically update our database and thus we can save our data. In certain cases we can store and backup our data in external hard disks or magnetic tapes and we can keep these in secure places and can update the database on demand.

In case of huge database normally the log files are backuping at regular intervals. I will have all the informations about the transactions made.

Generally the data backup includes Physical data backup and Logical data backup. The physical data backup includes physical files like data files, log files, control files etc whereas the Logical backup includes data like tables, views, procedures, functions etc. Logical data backup alone is insufficient to recover the data as it provide only the structural information.

Volume Shadow Copy Service- VSS

It is an infrastructure on Windows server platforms which enables applications to generate shadow copies of the database.

A shadow copy is a consistent snapshot of the data held on a volume or component at a well-defined point in time. A shadow copy set is a collection of shadow copies which are all taken simultaneously. Shadow copy Service identifies each shadow copy and shadow copy set by a persistent Global Unique Identifier (GUID).

In Volume Shadow Copy Service there is VSS requester, VSS provider and VSS Writer to implement the functionality.

A VSS requester is an application which requests the services to create shadow copies. VSS provider manages data storage volumes and generates shadow copies on demand. a provider generates in response to a requester,and creates and maintains this data copy until it is no longer needed. VSS writer is an application or a service that writes data to a disk and cooperates with VSS providers and requesters. During backups, writers ensure that data storage is in the proper state for a shadow copy.

Here attached pictorial representation of VSS
Restore Point

Restore point helps to use a table or database back to the time of creation of database or table. Normally there are two types of restorw points. Guaranteed restore points and normal restore points. The main difference between the two is the guaranteed restore points never age out of the control file and must be explicitly dropped.

Rollback

The rollback is a transactional command used to undo transactions which have not already been saved to the database. The rollback command can only be used to undo transactions since the last commit or rollback command was issued. IThe rollback command erases all data modifications made from the start of the transaction or to a savepoint.