The hardest part of a team to maintain from year to year is the bullpen, with unheralded pitchers breaking out one year and struggling the next, which has general managers reaching for the antacid tablets.

There are plenty of question marks when it comes to the bullpens in the National League West as we head into the final three weeks of Spring Training. Here's a look at what we know and don't know right now:

D-backs

The known: The D-backs added experience to their bullpen by signing Joakim Soria just before Spring Training started and Tyler Clippard not long after camp opened. The pair will combine with Stefan Crichton, who finished 2020 as the team's closer, to handle the backend of games. While the team has said that Soria is competing with Crichton for the closer's role this spring, it seems a good bet that Soria's experience and track record will likely mean he gets the first crack at closing.

The unknown: Just about everything else in the bullpen is up in the air with a lot of candidates competing for spots. Lefty Alex Young has a good chance to make the team while Yoan Lopez and Kevin Ginkel each have had their share of successes and struggles the past couple of seasons and have things to prove this spring. Taylor Clarke has been a starter throughout his Minor League career, but he could be kept for length. A lot depends on which younger pitchers the team chooses to keep in the Minors as starting depth and which they are willing to shift to the bullpen for 2021. -- Steve Gilbert

Dodgers

The known: Despite some of Kenley Jansen's struggles last season and his decreased velocity, Dodgers manager Dave Roberts made it clear that the 33-year-old will be the team's Opening Day closer. Jansen was at 88-90 mph in his last Spring Training outing, but the Dodgers aren't concerned with his velocity this early in the spring. Behind Jansen, Blake Treinen, Victor Gonzalez and Corey Knebel will provide plenty of coverage.

The unknown: Joe Kelly and Brusdar Graterol's availability is the unknown of the spring for the Dodgers. Kelly has been dealing with an undisclosed injury and time is against the right-hander to be ready for Opening Day. Graterol had some non-surgery issues during the offseason and came into camp slightly behind schedule. Graterol still hasn't pitched in a game, and it is becoming increasingly likely that he'll have to miss some time at the beginning of the season. If Kelly and Graterol are placed on the injured list, Dennis Santana and non-roster invitee Jimmy Nelson are possible options to join the bullpen. -- Juan Toribio

Giants

The known: The bullpen is the most unsettled area of the roster, but Jake McGee, Matt Wisler, José Álvarez and Jarlín García are probably locks to be with the Giants on Opening Day. McGee, Wisler and Álvarez were added on Major League deals this offseason, while García is out of options and posted a 0.49 ERA over 19 appearances in 2020. Tyler Rogers offers a different look with his unique submarine delivery, so he's also a solid bet to be part of the relief corps. Rule 5 Draft pick Dedniel Núñez has hit 97 mph with his fastball and boasts a "ridiculous" slider, stoking optimism that he'll be able to stick on the 26-man roster as well.

The unknown: Reyes Moronta logged a 2.66 ERA over his first three seasons in the Majors, but he's coming off right shoulder surgery and has yet to appear in a Cactus League game, creating questions about his readiness for the 2021 campaign. The Giants have a long list of other candidates for the final slots in their bullpen, including Wandy Peralta, Sam Selman and non-roster invitees Jimmie Sherfy, Jay Jackson, Silvino Bracho, Dominic Leone and Zack Littell. Caleb Baragar and non-roster invitees Nick Tropeano, Scott Kazmir and Shun Yamaguchi are being stretched out as starters this spring, but they're also candidates to serve as swingmen out of the bullpen if they're left out of the rotation mix.

Padres

The known: Drew Pomeranz, Emilio Pagán, Keone Kela and Mark Melancon will all see high-leverage roles in the late innings for the Padres. It's not entirely clear what those roles will be -- and they likely won't be pigeonholed into specific innings. But those four are set to anchor the 'pen, and it's a compelling mix. All four have spent time as closers in the past, and they all boast the stuff necessary to potentially fill the role in 2021.

The unknown: Those four are locks, with Pierce Johnson, Austin Adams and Craig Stammen almost certainly in as well. That leaves a competition for two places, and that competition has thinned significantly in recent weeks. José Castillo will miss the season due to Tommy John surgery, while Javy Guerra (UCL sprain) and Matt Strahm (October right knee surgery) are expected to open the season on the injured list. Among the candidates for the final two spots are Dan Altavilla, Michel Baez and Taylor Williams -- with starting pitching prospects Ryan Weathers and Adrian Morejon potentially available to move into the 'pen.

Rockies

The known: Last year, the Rockies' 6.77 bullpen ERA was highest in their history over a full season. But that may have been more 2020 weirdness than anything else. There's enough material here that turnaround in terms of health and performance, which could make the Rockies a surprise competitor. Closer Daniel Bard will be trying to build on his National League Comeback Player of the Year Award performance, Scott Oberg returns after missing last season with blood clots and Jairo Díaz (slowed by a COVID-19 diagnosis) and Carlos Estévez (bruised right hand) are back after pitching last year hurt. Add Mychal Givens and a couple other emerging righties, Yency Almonte and Tyler Kinley, and there is basis for optimism.

The unknown: One problem is good: Out-of-options trade acquisition Robert Stephenson and Rule 5 Draft pick Jordan Sheffield are under pressure to grab a spot. One problem may be vexing: Unless Phillip Diehl, Ben Bowden or Brian Gonzalez can pitch their way onto the squad, there won't be a lefty to start the year. One problem makes for tough decisions: Unless the Rockies shift a starter type like Chi Chi González or Dereck Rodríguez to the 'pen, there isn't a long reliever.