FSDB is a file system data base. FSDB provides a thread-safe, process-safe Database class which uses the native file system as its back end and allows multiple file formats and serialization methods.
Advantage:-
FSDB stores bundles of ruby objects at nodes in the file system.
The IEEE Verilog standard defines an ASCII text based Value Change Dump (VCD) that all simulators support. However, for any large simulation, the VCD format takes up too much disk space and is very slow. Most simulators store their signal databases in a proprietary binary format to speed things up and takes up much less disk space. You can only view the signals from these databases using the same tool that generated them. You can also buy additional tools that you can connect to your simulator that have their own signal dumping files and waveform viewers. That way you can use the same viewer regardless of the simulator you are using. Springsoft is one example of a vendor providing a tool that connects to your simulator and it outputs a binary FSDB file.
Fsdb is fast signal database ... Compare to all waveform dump ... it will be fast and takes very less space .... In my experience it took 30% of size normal dump and completed test with 20% more time than with no dump... You need to have debussy or nWave or Verdi or Siloti toold to view waveform ... Tool will have few utilities like fsd2vcd , vcd2fsdb converters , fsdbsplit etc ....