You must ensure there is enough space to store the dump under the mount point having directory location.
expdp
expdp user/pwd DIRECTORY=DIR_NAME DUMPFILE=full_db.dmp logfile=full_db.log FULL=y
impdp
expdp user/pwd DIRECTORY=DIR_NAME DUMPFILE=full_db.dmp logfile=imp_full_db.log FULL=y