Here's an example rotated log (Btrfs, NVMe, no compression, default ssd mount option). As you can see it takes up more space on disk than it contains data, so there's a lot of slack space for some reason, despite /etc/systemd/journald.conf being unmodified and thus Compress=Yes.
file: system@2547b430ecdc441c9cf82569eeb22065-0000000000000001-00054c3c31bec567.journal extents 41 disk size 143511552 logical size 100663296 ratio 0.70 $ sudo btrfs fi defrag -c system@2547b430ecdc441c9cf82569eeb22065-0000000000000001-00054c3c31bec567.journal And now: file: system@2547b430ecdc441c9cf82569eeb22065-0000000000000001-00054c3c31bec567.journal extents 768 disk size 21504000 logical size 100663296 ratio 4.68 That's nearly 1/7th smaller. The existing defrag without compression is probably just increasing write amplification on SSDs. If it's badly fragmented just leave it alone. This also works on nocow journals with +C set, although I'm not sure whether this is intended behavior (I thought nocow implies no compression); so I've asked about that on the Btrfs list. Chris Murphy _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
