SAP HANA is an in-memory database. The data is kept in the RAM of one or more SAP HANA worker hosts, and all database operations (reads, inserts, updates, and deletions) are performed in the main memory of the host. This feature differentiates the SAP HANA database from traditional databases, where only a part of the data is cached in RAM and the remaining data resides on disk.
Persistent storage ensures the ability to restore the SAP HANA database to its most recent committed state in case of failure. The log captures all changes by database transactions (redo logs), and data and undo log information is automatically saved to disk at regular savepoints.
As SAP-certified enterprise storage arrays for SAP HANA, Unity XT arrays 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 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 tables are 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. A standby host waits for a failure of a worker host so that it can take over its role, a process known as host auto-failover. Because the in-memory capacity 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 on SAP HANA. By default, SAP supports scale-out deployments of up to 16 worker hosts. If more than 16 worker hosts are needed, SAP requires a site-specific certification.