The IBM jdbc drivers can be run in Type 2 (native) or Type 4 (pure Java). By
default, Type 2 seems to be used.
Type 2 is much more restrictive, since native libraries are required. Different
libraries are used for each platform, and certain platforms (e.g., MacOS) appear
not to be supported at all.
The IBM drivers are the only ones that are supported in Type 2.
Unless there are additional mitigating factors, the drivers should be used in
Type 4 by default.