Nightly rsync and the heat problem
When I first set up a nightly cron job to copy my home directory to an external SSD, the laptop’s fan stayed at full blast all night. The CPU hit 90 °C, and the battery life dropped noticeably. I blamed the SSD’s sluggish write speed, but the real culprit turned out to be the I/O scheduler giving the backup process too much priority. Adding ionice -c3 (the idle class) to the rsync command brought the temperature back to sane levels without sacrificing backup reliability.