The following SAP HANA system replication modes exist:
| Mode | Details | Behaviour when secondary system is not available |
| Synchronous | Primary system waits until secondary system has received data and persisted it to disk. | Primary system waits until global.ini -> [system_replication] -> logshipping_timeout is exceeded (default: 30 s) and then proceeds without replicating data. |
| Synchronous in-memory | Primary system waits until secondary system has received data. | Primary system waits until global.ini -> [system_replication] -> logshipping_timeout is exceeded (default: 30 s) and then proceeds without replicating data. |
| Synchronous full sync (SPS 08 and higher) | Primary system waits until secondary system has received data and persisted it to disk. | Primary system is blocked until secondary system becomes available. |
| Asynchronous | Primary system doesn't have to wait for secondary system (unless the asynchronous log buffer is full and waiting is configured, see "Can problems with system replication impact the performance on the primary system?" in note 1999880) | Primary system proceeds without replicating data. |