Shitty fuck balls.
In the shite weather weekend before last there was an unusually long power cut. My UPS ran down which triggered my server to shut down gracefully and my desktop to shut off with no grace at all. Getting the server (serial connected to the UPS) to shut down the desktop is a job still on the todo list. Ho hum.
This resulted in an unbootable desktop, BTRFS parent transid failure which means the disk filing system has errors in it. Potentially a total data loss, poo. A day of careful fettling later I had recovered the data and imaged the drive so I ran a repair which worked, phew. Most stuff is backed up but it would have been inconvenient to lose and inconvenient to have to reinstall.
This morning the server is not responding, BTRFS parent transid failure. No power cuts this weekend, no reason for it to have rebooted, no reason for it to have suffered corruption. WTF?