An SAP HANA system is composed of three main components:
- The host
- The system
- The instance
Host:
A host is a hardware server or operating environment in which the SAP HANA database runs. The host comprised of CPU, memory, storage, network, and operating system.
The host provides links to the installation directory, data directory, and log directory, or the storage itself. The storage for an SAP HANA installation does not have to be on the host.
For multi-host systems, a shared storage or a storage that is accessible on-demand from all hosts is required. For more information, refer to the multi-host system concepts.
Instance:
An SAP HANA instance is the set of SAP HANA system components that are installed on one host. A system can be distributed as several instances among several hosts, but each instance in a multi-host system must have the same instance number.
System:
A system is one or more instances with the same number. The term "system" is interchangeable with the term "SAP HANA database". If a system has more than one instance, it must be dispersed over several hosts as a distributed system.
An SAP HANA system is identified by a System ID (SID), which is a three alphanumeric character designation that provides a specific nomenclature for a particular SAP HANA system.
From the perspective of a system administrator, SID is one unit, which can be, started up, shut down, or backed up the system as a singular entity. While data itself can be divided amongst the memory of the different hardware servers which makeup the SAP HANA system
An SAP HANA system can be configured as one of the following types:
Single-Host System:
If there is only one host in a system, it is called a single-host system.
A single-host system have only one operating system environment to install an SAP HANA system.
A single-host system is the simplest system installation type. It is possible to run an SAP HANA system entirely on one host and then scale the system up as needed.
Multi-Host Systems:
If there are multiple hosts in a system, it is called a multiple-host (or distributed) system.
A multiple-host system is a system with more than one host.
A multi-host SAP HANA system is where the instances of an SAP HANA SID are installed on more than one hardware server, but work together.
A multi-host (also called distributed) system is used to spread the load over several hosts. To add hosts to an existing system, SAP HANA lifecycle manager (HLM) tool is used.
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