tmpfiles: Add +C attrib to the journal files directories Add the +C file attribute (NOCOW) to the journal directories, so that the flag is inherited automatically for new journal files created in them. The journal write pattern is problematic on btrfs file systems as it results in badly fragmented files when copy-on-write (COW) is used: the performances decreases substantially over time. To avoid this issue, this tmpfile.d snippet sets the NOCOW attribute to the journal files directories, so newly created journal files inherit the NCOOW attribute that disables copy-on-write. Be aware that the NOCOW file attribute also disables btrfs checksumming for these files, and thus prevents btrfs from rebuilding corrupted files on a RAID filesystem. In a single disk filesystems (or filesystems without redundancy) it is safe to use the NOCOW flags without drawbacks, since the journal files contain their own checksumming.