Since the Pellegrini era there's been little turnover within Madrid's defense (especially so relative to the rest of the squad). Marcelo, Pepe, and Sergio Ramos have over 700 starts combined, most of which have come alongside one another. Real Madrid has found success in scooping up young, unpolished defenders and gradually phasing them into the first team (see: Marcelo, Varane, Ramos), and that practice continued with the signing of Danilo.
By last season's numbers
The most popular defensive stat is goals conceded, but like most metrics, it has its limitations. For example, Rayo Vallecano always, always concede some of the most goals in the league, yet are never in danger of being relegated (Their manager Paco Jémez is a maniac and a beacon of entertainment in football). Levante coughed up the second most goals last season, and finished comfortably in 14th. Allowing many goals does not necessarily doom a team, but when the margin for error in La Liga is so thin, Real cannot afford to have allowed 17 more goals than Barça as they did a year ago. Real Madrid conceded the fifth fewest goals in La Liga (At 38, Real were pretty far off from Barcelona's 21, and very far off from Rayo and Córdoba's 68).
Real were middling in shots against per game (12th place, allowing 11.9 per game). Real ranked 19th in tackles per game, and were dead last in interceptions per game (though these particular stats' deviation are much smaller, and are likely a product of Ancelotti's opportunistic, absorbing defending style). With the arrival of Rafa Benítez, whose reputation for stingy defending precedes him, the expectations for Real's back line have been amplified.
But enough about last season! Let's talk about...flawed stats from...totally meaningless preseason games! Real Madrid have conceded only 2 goals all summer! That's fewer than any preseason in the last 10 years! That's gotta count for something, right? Maybe a little bit? No? Okay. Let's look at the players making up Benítez's back line.
Marcelo: Marcelo is becoming an exaggerated version of himself. Over the years, he's gotten better in attack and worse in defense. A magnate of poor positional discipline, Marcelo will likely start the lion's share of matches at left back. His pace hasn't waned even slightly, and his linkup play with Ronaldo is gamebreaking. If Marcelo ever gets dropped from Benítez's starting 11 it will be because he's picked up a knock, or because he's allowed a few too many opposing wingers to run around him.
Fábio Coentrão: Lost in the constant transfer rumors and injury reports is Coentrão's actual ability. He's the anti-Marcelo, a skilled tackler and man-marker who has a propensity to play his best in the spring's biggest matches. Perhaps he was brought in to be a rotational player in 2011, but his cap total for Real is a shockingly-low 55 matches. Whether he'll wear the Real Madrid shirt in 2015 is unknown, but if he stays and stays healthy, Coentrão is the type of player I could see Benítez loving.
Sergio Ramos: Now that he's essentially told Manchester United to go kick rocks, Ramos is set to head into 2015-16 as Real's new captain. His defensive ability is well-documented, and there is no reason to believe he'll be a regular liability going forward. And despite having the all-time La Liga records for most yellow AND red cards locked down, he managed to finish last season without a red card! You go, Sergio! One of the world's best defenders in the air and in attack (Ramos has scored at least 3 goals every season at Madrid, a solid mark for a defender), Sergio Ramos should continue to do Sergio Ramos things.
Pepe: Ever since turning the corner of 30, Pepe's decline has been anticipated, but if anything he's surged in the latter stages of his career. Bracketed by the likes of Varane, Ramos, and Carvajal, his lack of pace has been hidden and he's been flourishing as a distributing anchor in central defense. His disciplinary record has been plummeting in recent years, and he's perhaps the only Real Madrid to defender to consistently avoid costly mental lapses. He's set to miss the La Liga opener with a minor injury, but the questions around Pepe will remain the same: Can he stay healthy, and will Varane steal his job?
Nacho Fernández: Players who are content knowing they'll never crack their club's starting 11 are hard to find, and Nacho's embracing of this role has turned him into a fan-favorite. He's played both right and left back in emergency situations, and is as good of a fourth-choice center back as you can ask for. Nacho might get the nod in a Copa game or two, but he'll likely only see the La Liga pitch after the hour mark against inferior sides.
Raphael Varane: The world was introduced to Varane in 2012 and he earned the nickname "Don Limpio" or "Mr. Clean" for his lack of mistakes. Though the nickname hasn't stuck, he's lived up to it -- no one on Real Madrid had more clearances than Varane, he commits the fewest fouls on the entire team (not just among defenders), and he picked up only one yellow card in all competitions last season. He's singlehandedly solved Real's Argentinian problem basically becoming the
Magic Messi Eraser (Messi has scored only one goal from open play or assisted a goal while Varane was on the pitch), and as alluded to earlier it's a matter of when, not if, Varane will take Pepe's spot in the first 11. At times he relies a bit too much on his length and not tackling ability in one-on-one situations, but under Benítez he'll be set to continue his development.
Álvaro Arbeloa: At this point in his career, The Spartan is less a squad player and more a motivator, and like Nacho, he seems okay with it. Since Carvajal's return from loan, Arbeloa has been relegated to the bench and he dropped yet again with the arrival of Danilo. Even as recently as this week Arbeloa's been linked to MLS, so it's unlikely we'll see much of No. 17 on the pitch in 2015.
Dani Carvajal: The alarming thing about Carvajal is how in his two seasons as a starter in Madrid his fouls per game number has remained steady, but last year he collected 13 yellow cards, a considerable jump up from six in 2013. He spent 2014 growing both his beard and temper, and while Danilo may have been brought in regardless of Carvajal's play, the Madrid youth product will have to fend off Danilo for minutes in 2015. The good news for Carvajal is most of his issues exist from his shoulders up, and he's still an athletic battering ram on the right wing.
Danilo: Here's what we know about Danilo. He's built like a truckhouse. He has center back height, but plays on the right, and shoots with his left. Brazil boss Dunga compares him to Maicon. What we don't know is how Benítez plans to use him, or how much for that matter. It's hard to imagine a scenario in which either he or Carvajal is pencilled in as the undisputed starter, so he'll probably see plenty of the pitch. We just have to sit back and see what the electric Brazilian can do.