siebns.dat
In siebel bookshelf, it is mentioned that siebns.dat file gets stored at <gateway_root>/admin directory and enterprise information continiously get flushed to the siebns.dat file and keeps 5 backups of this file. In my environment :
When I execute 'backup nameserver', a new back of siebns.dat file is created in <gateway_root>/admin directory but I can see that the siebns.dat file which is being used and updated during enterprise runtime is not from this directory and it in <gateway_root>/sys directory. Five backups are also being placed here and getting continously updated and backed up.