Alter a big table

Hi all, in a table with logging and fragmentation by round robin I have to add two columns at the end: alter table xxxx add (yyy smallint, zzzz money(8,2)); The table contains about 171,000,000 with a row size of 650 byte. In my testing-system with nearly the same number of rows the alter table statement lasted unter a minute but with LTAPEDEV=/dev/null. My question: In the production system LTAPEDEV points to an existing device. Could it happen that the alter table needs much more time to execute and/or that we'll run in a long transaction? TIA Reinhard