Traders signal offers in the Standard & Poor's 500 stock index options pit at the Chicago Board Options Exchange (CBOE).

Chicago Board of Options Exchange staff knew of problems with software hours before the glitch caused a half-day outage, but they thought they could fix them, the Wall Street Journal reported on Friday, citing people briefed on discussions.

CBOE officials have been looking into whether the exchange should have moved to its backup trading system instead of relying on staffers' ability to get the main system online, the report said.