Slow import for users .DMP files in Oracle 11G After upgrading my DBMS Oracle 10g to 11g, when it will import user files, they are slower than the old version.

A .DMP file in Oracle 10g with the size of 20GB takes almost 1 hour to import, but Oracle 11g version takes almost 3 hours for the same .DMP file.  

Export script:

NLS_DATE_FORMAT='dd/mm/yyyy hh24:mi:ss' ; export NLS_DATE_FORMAT
NLS_NUMERIC_CHARACTERS=',.'; export NLS_NUMERIC_CHARACTERS

exp system/datapar1 file=copy.dmp log=exp.log owner=username \
    buffer=4096000 recordlength =65535 statistics=none \
    feedback=500000 consistent=yes


Import script:

NLS_DATE_FORMAT='dd/mm/yyyy hh24:mi:ss'; export NLS_DATE_FORMAT
NLS_NUMERIC_CHARACTERS=',.'; export NLS_NUMERIC_CHARACTERS

imp system/password file=copy.dmp log=imp.log fromuser=username \
    touser=newusername ignore=yes


Could anyone help me with this?
It could be that one of the imp default parameters for Oracle 10G is different in Oracle 11G.  I would try adding the

buffer=4096000


parameter to the imp command to see if that helps.  That parameter is available on both exp and imp commands.