One of my first impressions with RedHat based Distros was that I couldn’t just plug in a thumb drive and mess with the partitions from the installed OS. Why? Because I got this “Device or resource Busy” error, in other words: someone else was using that drive already, and to please stop them and Linux would be glad to do that thing for me.
Fast forward about a year and some searching dug up the lsof command. Lovely, lovely command. It helped me find the enemy, and the enemy was me? Yup. root was the, erm, root of the problem. But it didn’t help me figure it out. It wasn’t until today, when I was researching raid levels and set up, that I discovered the issue: multipath.