big database with very small dump !?

Hello all,

        I'm finding it very strange that my pg takes 9Giga on disk but
        pg_dumpall produces a 250Mega dump. 'VACUUM FULL' was executed
        yesterday.

        Is this normal ? Should I be worried ?


        details bellow:
        ------------------------------------------
        # pg_dumpall --oids --clean > pg_dumpall.sql
        # ls -lh
        total 232M
        -rw-r--r--    1 postgres postgres     231M Aug 11 15:46
        pg_dumpall.sql
        # du -sh /var/pgsql/data/
        9.4G    /var/pgsql/data
        ------------------------------------------


        thx
        joao