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SAP HANA is an in-memory database, meaning the data is kept in the main memory of one or more SAP HANA worker hosts (active components that accept and process database requests). This feature differentiates the SAP HANA database from traditional databases, in which a part of the data is cached in memory and the remaining data resides on disk. With SAP HANA, all database operations (reads, inserts, updates, and deletions) are performed in the main memory of the host.
Persistent storage can restore the SAP HANA database to its most recent committed state in a failure scenario. The log captures all changes by database transactions (redo logs). Data and undo log information is automatically saved to disk at regular savepoints; the default is five minutes.
As a certified enterprise storage system for SAP HANA, PowerFlex File storage can be used for both single-host (scale-up) and multihost (scale-out) systems in TDI deployments.
In single-host environments, the database must fit into the memory of a single server. Single-host environments are preferred for OLTP-type workloads such as S/4HANA and SAP Business Suite on SAP HANA.
In multihost environments, the database tables are distributed across the memory of multiple servers. These environments use both worker and standby hosts. The worker hosts accept and process database requests, while standby hosts have the database services running but have no data in memory. A standby host waits for a worker host to fail and then takes over the worker host’s role, a process known as host autofailover. Because the in-memory capacity in these deployments can be high, scale-out SAP HANA clusters are suited for OLAP-type workloads with large datasets, such as SAP Business Warehouse on SAP HANA and SAP BW/4HANA. By default, SAP supports scale-out deployments of up to 16 worker hosts. If more than 16 worker hosts are needed, a site-specific SAP certification is required.