Although the story is clearly fictional, there has been a similar case of prison break in real life.
"Alcatraz Island", in San Francisco, which is known for being the best prison for the most scary and dangerous felons. In 1961, three felons started digging holes on the walls of their cells with spoons, nail clippers, and coins. They even refitted a vacuum cleaner as an electric drill. They thought everything through, they even managed to silence the sound of the tools by playing the accordion and covered the holes with newspapers, so that prison guards were completely fooled. With no apparent further obstacles, the three felons escaped from prison. However, to the day, the Alcatraz prison claims that they drowned trying to escape.
The film tells the story of a bank robber who is caught and imprisoned in Alcatraz. He works in the library there. Luckily, nobody knows he is secretly planning a prison break...
The male protagonists are all targeted by gays inside the prison.
They all hide their tools inside Bibles.
They both have a black friend.
And their wardens are similarly vicious...
However, why does nobody know about the existence of Escape from Alcatraz? It might be because it was released a long time ago and it was filmed in documental format. I belive the success that followed The Shawshank Redemption is mainly because it's a movie and those are more easily accepted by the audience.
To sum up, The Shawshank Redemption is fictional, but it was heavily inspired by Escape from Alcatraz, which, in turn, was also inspired by something else, in this case, these very real felons who allegedly died escaping Alcatraz.