SAP HANA Operation modes

 

Operation mode	SAP HANA Version	Description	Advantages
delta_datashipping	no restriction	Synchronization between primary and secondary site is implemented via regular delta data shippings from primary to secondary site.	Memory footprint of secondary site can be smaller as column store tables don't have to be loaded during system replication As a consequence it is possible to set the global_allocation_limit (SAP Note 1999997) and run an additional non-production system on the same machine. History tables are generally supported (for logreplay modes the restrictions described in SAP Note 2480889 apply)
logreplay	>= 1.00.110	Synchronization between primary and secondary site is implemented purely based on redo logs Column store generally has to be loaded into memory to provide reasonable delta merge speed	Delta data shipping no longer required Reduced network traffic between primary and secondary site Reduced network bandwidth requirements between primary and secondary site Reduced takeover times (shorter log replay, no persistence garbage collection, no file ID mapping and disk LOB initialization, no adjustment of resource container dispositions; see SAP Note 2222217) No propagation of logical persistence corruptions on disk level (e.g. introduced by the bug described in SAP Note 2375691)
logreplay_readaccess	>= 2.00	Synchronization between primary and secondary site is implemented purely based on redo logs Column store generally has to be loaded into memory to provide reasonable delta merge speed See SAP Note 2391079 for restrictions.	Same advantages like "logreplay" above Query load can be moved away from primary site

The operation mode can be checked from the following parameter:

global.ini -> [system_replication] -> operation_mode

They are defined by “hdbnsutil -sr_register –operationMode= …” command. 

In 3-tier environments the following details can be considered for the logreplay mode:

• If the tertiary system is down, the logs are only saved on the secondary system, not on the primary system.
• If the secondary system is down and you want to use the tertiary system as secondary system, usually a full sync is required, because the logs retained on primary site are meant for the secondary site and so they may not be compatible with the tertiary system.

SAP Note 2661878 provides settings that can be used to optimize the performance of logreplay on secondary system replication site. These settings are a trade-off between logreplay performance and memory utilization and secondary site, so tests are required in order to identify an optimal compromise.