Comment 5 for bug 1942935

Similar report here on 5.10.0-rc4:
https://www.spinics.net/lists/raid/msg66654.html

I ended up masking the services introduced with 20.04 LTS, and switched back the crontab.

systemctl mask mdcheck_continue.service mdcheck_continue.timer mdcheck_start.service mdcheck_start.timer
cat > /etc/cron.d/mdadm << 'EOF'
#
# cron.d/mdadm -- schedules periodic redundancy checks of MD devices
#
# Copyright © martin f. krafft <email address hidden>
# distributed under the terms of the Artistic Licence 2.0
#

# By default, run at 00:57 on every Sunday, but do nothing unless the day of
# the month is less than or equal to 7. Thus, only run on the first Sunday of
# each month. crontab(5) sucks, unfortunately, in this regard; therefore this
# hack (see #380425).
57 0 * * 0 root if [ -x /usr/share/mdadm/checkarray ] && [ $(date +\%d) -le 7 ]; then /usr/share/mdadm/checkarray --cron --all --idle --quiet; fi
EOF

The pausing and resuming of the integrity check was an annoyance for me anyways.