After going behind early on through Anthony Pilkington's cool finish, the Millers turned it around in south Wales as Joe Newell and Pilkington's own goal either side of half-time gave them a 2-1 lead.
That was short-lived, though, as Pilkington got back to doing the business at the right end but firing in an equaliser.
The Millers more than held their own and boss Redfearn felt they could have won it.
"I’m really pleased with the performance," he said. "To come away with something when you visit Cardiff is no mean feat.
"Perhaps the only disappointment is that we should have won with the way we got ourselves in front and how we played second half.
"It was a good football game, although it took a while to come to life. We started slow and they got their goal which was disappointing.
Cardiff boss Russell Slade also felt his side should have been celebrating the win and played down the Millers' impact in the game.Cardiff v Rotherham: https://t.co/tfX84hPmzy via @YouTube— Rotherham United (@OfficialRUFC) January 24, 2016
"We are not going to have too many more opportunities like that before the season ends and of course that is very frustrating.