Hi Benedict,
As explained by Mayuresh above, it depends on HANA Landscape.
Different Hardware partners have implemented High Availabality differently as IBM uses GPFS(General Parallel File System) - a shared disk clustered file system developed by IBM itself while HP, Fujistsu use different implementation.
You can also check the following documents:
http://www.saphana.com/docs/DOC-2935
The below whitepaper is from Oracle on their Analysis of HANA High Availabilty:
http://www.oracle.com/technetwork/database/availability/sap-hana-ha-analysis-cwp-1959003.pdf
Regards,
Vivek