Good reasons NOT to use a relational database?

Question

Can you please point to alternative data storage tools and give good reasons to use them instead of good-old relational databases? In my opinion, most applications rarely us

Answer 1

Custom (hand-written) storage engine / Potentially very high performance in required uses cases

http://www.hdfgroup.org/

If you have enormous data sets, instead of rolling your own, you might use HDF, the Hierarchical Data Format.

http://en.wikipedia.org/wiki/Hierarchical_Data_Format:

HDF supports several different data models, including multidimensional arrays, raster images, and tables.

It's also hierarchical like a file system, but the data is stored in one magic binary file.

HDF5 is a suite that makes possible the management of extremely large and complex data collections.

Think petabytes of NASA/JPL remote sensing data.