In three appearances this year, White has allowed 11 runs, 10 hits in just 3.2 innings of work. Still, the Mariners feel he can help put the team in a better position as the season moves along.
"We've had our eye on White for a long time, going back to last winter," assistant general manager Lee Pelekoudas told the Tacoma News Tribune in Saturday's edition. "He has three average pitches we think could become plus pitches."
In return, the Mariners sent minor league outfielder Sheldon Fulse, a 1999 third-round draft pick who starred as a shortstop in high school, to the Red Sox.
To make room on the 40-man roster, Seattle designated the recently acquired Cristian Guerrero for assignment.
Guerrero was picked up by the Mariners from the Brewers organization three weeks ago when Seattle designated outfielder Kenny Kelly for assignment. Kelly cleared waivers, returned to Tacoma, but is no longer on the 40-man.
Carrara has struggled mightily at times during the season, but may very well be retained since Mateo can still be optioned to the minors without having to clear waivers first.