Penney appears to be leaving Munster in good hands - the province are in the European Cup quarter-finals and currently sit second in the RaboDirect PRO12, a point behind Leinster.
And O'Callaghan, who recently became Munster's record appearance holder, surpassing the previous mark set by Ronan O'Gara, is convinced Foley will be a hit.
"He'll be an incredible coach. I'm lucky that I've played with Axel and I've always felt that he's been a coach on the pitch," second row O'Callaghan said.
"He always made the smartest reads in defence, he always knew exactly what to do at the right time. "He's Munster to the core. It's in his DNA. So it's going to be great, because we'll have a Munster man who knows us inside-out."
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