I've been running linux generally, and Debian specifically for years and I have never seen a bigger cluster f&(% than systemd. I'd gotten lazy with one of my most recent setups of Debian Jessie and allowed the cancerous systemd to be installed...and regretted it.
What follows is my setup and what happened:
I have a machine set up to store recorded hdtv shows on btrfs. It runs a minimal XFCE desktop as I can't stand Gnome. An hour show is about 5GB and I have about 100 shows at any given time. The directory where the shows are stored is bind mounted to where my nfs exports are and it is exported as read only for a KODI client to view. I never had any trouble with this setup under Wheezy, but under Jessie with systemd I ran into an issue when clearing out old recordings. First, deleting them through Thunar took forever, and when deleting multiple files at the same time the weird shit started. A few of the files would get deleted, but at some point I'd get an error that the file couldn't be deleted because it was read-only. Skipping it would give the error on every subsequent file. Opening a terminal and running mount revealed that the entire root filesystem had been remounted read-only! Attempts to remount it read-write failed. Nothing relevant shows in the logs. Rebooting would begin normally but at some point (usually the point nfs exports are started) I'd see a btrfs error flash past and the system would stop booting, or it might make it all the way to a login prompt (but no X11). Logging in would reveal the entire root filesystem is irrevocably mounted read-only. Booting from a rescue disk and checking the btrfs filesystem reveals no problems. Rebooting the system repeatedly eventually will randomly allow it to make it to X11 normally like nothing ever happened! The next time I would clean multiple files off, the same thing would happen. The only recovery is a random number of reboots. One time it took nearly 20!
After that I was pissed off enough to completely remove systemd and replace it with sysvinit. Guess what? No problems ever since. I can delete any number of files without any slowdowns or bizarre remounting of my entire system as read-only without so much as a log message. My btrfs checks always come back clean.
F systemd !