> I have made a load balancing (lvs) between two firebird server who
> can access on a unique gdb file shared by a nfs server.

Accessing an file on an NFS server is disabled by default. An single
Database file must not be accessed by differend Server-Instances. On
Super-Server access should be excluded by exclusively opening the
file, on Classic-Server the file is opened in shared mode but access
is coordinated by an server process.

> After a certain time my database file appears to be corrupted...

It should be corrupted rather shortly.

> Is anyone have made a load balancing solutions of firebird servers
> on a single gdb file without any corruptions??

You might try out replication to synchronize two copys of your
database. Without DB-Copys on differend harddsik you will presumably
have no gain since the DB-Server mostly is IO-bound, not CPU-bound.

Elmar