- HP Unix OS.
- Oracle Database Server to handle more than 150 million voucher details (each voucher may contain 512 bytes).
- My Web application should support about 5,000 simultaneous users.
Since your requirement limits you to HP-UX, then you will need a Unix server from Hewlett Packard. I would talk with the vendor to ensure that they spec out a good server for you.
The Oracle database will be able to handle 150 million rows of data. What will make a difference is the queries that touch the 150 million rows of data. If those queries are not optimized, the queries will not run fast. And you may need to employ partitioning to improve query performance.
Five thousand concurrent users can pose a problem. If they all connect to an application server, then make sure that the application server supports connection pooling. You may also need to use shared server on the Oracle database side of things to support many concurrent connections.
I would work with the HP vendor to scope out your I/O, memory and CPU requirements. Those will drive the server you will need to procure. HP has plenty of resources to help you with this.