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SAP HANA is an in-memory database. The data is kept in the RAM of one or multiple SAP HANA worker hosts, and database operations are performed in the main memory of the host. This feature differentiates SAP HANA from other traditional databases, where all data resides on disk and only the current working set is cached in RAM.
SAP HANA uses persistent disk storage to provide a fallback if a failure occurs, ensuring that the SAP HANA database can always be restored to its most recent committed state. The in-memory state of the database is persisted every five minutes to the disk using the savepoints method. Also, all transactions since the last savepoint are captured on disk in redo logs.
As a SAP-certified enterprise storage array for SAP HANA, the PowerMax system supports both single-host (scale-up) and multihost (scale-out) SAP HANA systems in TDI deployments.
In single-host environments, the whole database must fit into the RAM of a single server. Single-host environments are preferred for online transaction processing (OLTP)-type workloads, such as SAP Business Suite on SAP HANA.
In multihost environments, the database is distributed across the RAM of multiple servers. Multihost environments use worker and standby hosts. A worker host is an active component that accepts and processes database requests, while a standby host is a passive component that has all database services running but no data in RAM. The standby host waits for a failure of a worker host so that it can take over its role, a process known as host autofailover.
Because the in-memory capacity requirements in these deployments can be high, scale-out, SAP HANA clusters are perfectly suited for online analytical processing (OLAP)-type workloads with very large datasets, such as SAP Business Warehouse (BW) on SAP HANA. A multihost installation can be extended by adding new worker hosts to the system.