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Storage in SAP HANA, Backup and Recovery : This article covers the Storage in SAP HANA, Backup and Recovery. The SAP HANA database holds the bulk of its data in memory for maximum performance, but also uses persistent storage to provide a fallback in case of failure. Data backups are required to protect against data loss due to disk failures or logical errors.
Storage Backup and Recovery in SAP HANA
1. Storage in SAP HANA
The SAP HANA database holds the bulk of its data in memory for maximum performance, but also uses persistent storage to provide a fallback in case of failure. Data is automatically saved from memory to disk at regular save points. All data changes are also captured in the log. The log is saved from memory to disk after each committed database transaction. After a power failure, the database can be restarted like any disk based database and returned to its last consistent state by replaying the log since the last save point.
Storage and Backup in SAP HANA
The Persistency Layer is responsible for the durability and atomicity (ACID- compliance) of transactions. It manages data and log volumes on disk and provides interfaces for writing and reading data that are leveraged by all storage engines. The persistency layer ensures that the database is restored to the most recent committed state after a restart and that transactions are either completely executed or completely undone using a combination of write-ahead logs, shadow paging, and save points. Thus the persistence layer manages logging of all transactions and manages both row and column stores as well as save points and logging of all database transaction since the last save point.
HANA DB uses the multi version concurrency control (MVCC) principle for concurrency control. This enables long-running read transactions without blocking update transactions. MVCC, in combination with a time-travel mechanism, allows temporal queries inside the Relational Engine.
2. Backup & Recovery
Data backups are required to protect against data loss due to disk failures or logical errors. Data protection due to power failures are provided by save points and log writing. Back up provides the data protection when the persistent storage is damaged. Data backups need to be performed regularly and the system is available as usual during backups. Data backups can be executed using the SAP HANA studio, DBA Cockpit or scheduling using SQL statements.
The SAP HANA database automatically carries out log. The configuration files -.ini files- which contain the SAP HANA database configuration settings are not backed up as part of the database backup. If there are customer specific configurations, this also has to be backed up for restoration during a failure.
A recovery is required when the data area and log area are unusable or where there is a logical error. SAP HANA database can be recovered using data and log backups, log entries from the log volumes.
Following recovery types are available:
Recover the database to its most recent state using the most recent data backup, Log backups and Log area.
Recover the database to the following point in time using the last data backup available before the specified point in time, Log backups and Log area.
Recover the database to a specific data backup using the specified data backup.
Recover the database to the following log position using the most recent data backup available before the specified log position, Log backups and Log areas. This is the most advanced recovery option.
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