Hi Evgeniy
I had a similiar situation a while back where by i did an online export of the oracle database using consistent=y flag.
You still need to do this in low activity time, or you can use sapinst as well but do not tick the option that states stop running sap system, problem is that the export is not consitent because of database being changed the whole time.
Best option will be as suggested by Orkun to use parallel but will cause some locks
Best Regards
Marius