So, yes, journald does in fact do bulk copies of log files on rotate. btrfs is hardly some fringe FS and its COW-flag behavior is documented and well-known. I'd expect extensive work on journald's storage engine to have uncovered this behavior at some point.

> When did this become a discussion limited to journald on btrfs?

btrfs is in the HN thread title.

> and that seems like something btrfs should fix at some point

Amazing. The Linux kernel should change to work around journald's inflexibility?

What someone should fix at some point is journald's strange IO patterns and hard-coded "helpful" attribute changes. I'd rather it just rename the file and let me do any defrag/compression/flag-setting I want than do anything with chattr behind my back in ways I can't even configure.