To stop a process using a lot of CPU and I/O, set its niceness to 19 and its I/O niceness to “idle”.
Directly on the command line
ionice -c idle nice -n 19 cabal v2-build (or whatever)
Via top and iotop
top: press r to renice a process (to 19)
iotop: press i to reionice a process (to idle)