This ain’t hard time.

Fat-cat financial felon Raj Rajaratnam is kickin’ it big in the Big House — with a personal “manservant” at his beck and call, a prison insider tells me.

“He’s reigning like a king,” said the source of Rajaratnam’s new digs at the Federal Medical Center Devens, in Ayer, Mass., where he’ll spend the next 11 years on an insider-trading conviction.

“He’s doing his time in the lap of luxury compared to the other inmates.”

I’m told the one-time high-flying Manhattan billionaire has snagged a prime cell in Unit P3, the top floor of Devens’ hospital ward — usually reserved for the most seriously ill inmates.

What’s more, the source tells me, Raj “has a very delightful guy doing all sorts of stuff for him — sort of like a ‘manservant.’ When Raj needs something, this guy gets if for him.”

The manservant is a “gentle giant,” an American Samoan named Eddie, whose main job in the P3 unit is to push wheelchair-bound prisoners. He got himself transferred to P3 after befriending Raj, according to the snitch.

“He became enamored of Raj, and Raj started talking about how much he once paid his chauffeurs. Now Eddie wants to be Raj’s driver when he gets out,” the insider told me.

He even cooks for Rajaratnam using a nearby microwave when the fallen financier doesn’t want to hoof it to the dining hall.

P3 residents have private toilets, a shared balcony for sunning themselves, televisions and adjustable beds. The doors aren’t locked — but neither are they in most of the buildings at the Devens facility, according to my source.

The three floors in the “P” facility, including Rajaratnam’s, are usually reserved for the very elderly and those who are crippled.

For perspective, famous old mobster John “Sonny” Franzese — who was born in 1917 and is in failing health — is housed on the same floor as the 56-year-old Rajaratnam.

My source is annoyed that other, sicker patients are being held in parts of the prison that require up to a half-mile walk to the hospital and to the chow hall.

All of Devens is a medical facility, although some of the ailments are mental and not physical. Some seriously dangerous people are jailed there, including Dzokhar Tsarnaev, the surviving Boston bombing suspect.

Rajaratnam, my source says, seems to get around fine. In fact, he’s lost weight and has been congenial with the other prisoners, although the help of his “manservant” makes mingling less necessary.

Where in the prison does Rajaratnam really belong? My source says that, for some reason, he’s not in with the general population that’s housed in Building H.

On H’s two floors, there are two prisoners to a cell. They use a communal bathroom and — as far as anyone knows — there are no manservants.

“He is getting special treatment,” said my source, who asked that his name not be used.

Of course, when the rotund rat does want to head to the chow hall, he has a very short walk, most of it through an enclosed walkway, to get food.

John Dowd, the fallen hedge-fund titan’s lawyer, didn’t bother to call me back. The US Bureau of Prisons won’t comment beyond confirming that Rajaratnam is being held in Devens.

At trial, Rajaratnam’s legal team claimed he is very ill and asked the judge for a lenient sentence. Manhattan prosecutors seemed to have their doubts about the extent of the illness and challenged Team Rajaratnam to release medical records.

Those records, turned over to the court, showed that Rajaratnam has diabetes and might need a kidney transplant — the procedure all diabetes patients may ultimately face.

Prosecutors didn’t seem impressed by those maladies when they sought a longer term than Rajaratnam suggested.

“Big deal,” my snitch said about the diabetes claim. “Up there, diabetes is like a common cold.”

So maybe now prison officials and Rajaratnam’s lawyers would like to discuss this. They have my number.

Until I’m convinced differently, Rajaratnam looks like a billionaire baby.