D and uninterruptable sleep

Htop

I recently have been having significant home server issues, and that's not the point of this - today I learned what D state is when looking at htop.

Apparently this means "uninterruptable sleep" and it's a dev's nightmare...

Context

The issue I was having was that some zfs rollback commands were hung - for hours... I wasn't sure what was going on, rollbacks should be instant but I figured it was just an artifact of these issues.

Turns out I still don't know what locked the disks up but I learned why <C>-c did nothing... the more you know