Here's quick info for you :
1. H2 is a Java based embedded RDBMS system as ThingWorx's Persistence provider, it's largely for maintaining lower disk foot print, you probably wouldn't want to go for it if you are looking for larger data sets to handle with, in the future. It's an open source RDBMS. No additional installation steps would be needed.
2. SAP Hana is an in-memory RDBMS system allowing you to perform very high speed parallel transactions as most of the data is stored in-memory (RAM), (bypassing the need to hit the HDD to larger extent) would recommend you to go through the documentation for this for more detail. Require additional installation step
3. PostgreSQL is another RDBMS system capable of handling ~500G of data, will require additional installation step
As to the scalability and high availability, in my opinion both SAP HANA and PostgreSQL would fall in this category. With PostgreSQL you have the option to setup High Availability on the database Layer, please check this documentation
Hope this would help.