From O'Reilly's "System Performance Tuning":

"In ansynchronous transfers, data can be transmitted at an arbitrary time; the receiver and the sender need not be clock-synchronized. This kind of transfer necessitates that EACH BYTE be acknowledged, which imposes a practical limit on transmission speed. In synchronous mode, transfers may only start at specific clock phases, but this alleviates the acknowledgement problem that ansynchronous transfers suffer from."

So why would RedHat default installed drives to asynchronous mode?

Pros, cons?