Buy vs. Build
The only choices here are what type of hardware and database to purchase, as there is basically no way that one can build hardware/database systems from scratch.
In making selection for the database/hardware platform, there are several items that need to be carefully considered:
Scalability: How can the system grow as your data storage needs grow? Which RDBMS and hardware platform can handle large sets of data most efficiently? To get an idea of this, one needs to determine the approximate amount of data that is to be kept in the data warehouse system once it's mature, and base any testing numbers from there.
Parallel Processing Support: The days of multi-million dollar supercomputers with one single CPU are gone, and nowadays the most powerful computers all use multiple CPUs, where each processor can perform a part of the task, all at the same time. When I first started working with massively parallel computers in 1993, I had thought that it would be the best way for any large computations to be done within 5 years. Indeed, parallel computing is gaining popularity now, although a little slower than I had originally thought.
RDBMS/Hardware Combination: Because the RDBMS physically sits on the hardware platform, there are going to be certain parts of the code that is hardware platform-dependent. As a result, bugs and bug fixes are often hardware dependent.
True Case: One of the projects I have worked on was with a major RDBMS provider paired with a hardware platform that was not so popular (at least not in the data warehousing world). The DBA constantly complained about the bug not being fixed because the support level for the particular type of hardware that client had chosen was Level 3, which basically meant that no one in the RDBMS support organization would fix any bug particular to that hardware platform.
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