He's recorded a season-high 11 sacks in 2015 and 2017.
It breaks Denver linebacker Von Miller's previous record deal of $19m (£14.7m) a year for a defensive player.
Donald, the 13th overall pick in 2014, had been entering the final season of his rookie contract, which is the same situation Mack - the 2016 AP Defensive Player of the Year - finds himself in with Oakland.
Donald, the reigning National Football League defensive player of the year, has recorded at least eight sacks in each of his four seasons with the Rams, including 11 last season. It was the second straight year he was holding out, though last season he reported to the Rams on the eve of the regular season.
Earlier this week, McVay said Donald should be able to play in the Rams' Monday night regular-season opener in Oakland on September 10 if he reached a deal with the Rams within the next few days.
"Getting him in here sooner than later, which is something that we do feel good about, is hopefully going to happen", McVay said Tuesday.
The Donald contract should help get things started for Mack and the Raiders, but let's see if they can come to a deal before the Week 1 opener against Donald's Rams.
Over his four-year career, Donald has compiled 39.0 sacks and 148 tackles.
"I don't really know anything else", McVay said with a laugh.
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