Before wiping I suggest making an image with btrfs-image. And then also see if any additional messages appear with the enospc_debug mount option. And also see if there's any correlation between the journald reported failures (the specific .journal file) and whether it's +C by using lsattr. Fedora 21 systemd journal files do not have +C by default, whereas Fedora 22 systemd journal files do use +C by default. So I'd expect the journal files to be a mix. Also let us know if there are snapshots that affect /var/log/journal (either reflink copies of the journal files or a snapshot of the root subvolume which contains /var/log/journal.
Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
