Single log line is 49KB+ (ext4) / 110KB+ (btrfs) of systemd-journald disk writes
A systemd issue documents severe write amplification in journald: one short log message can result in roughly 55 KB of writes, while 14 messages produced 386 KB of physical writes in a controlled test. The report attributes the overhead to journald’s mmap-based, indexed on-disk format and shows a much smaller append-plus-sync text-file baseline.
A follow-up measurement found journald writes persistently on each message and only delays fsync with SyncIntervalSec; a former journald contributor connected the behavior to small, scattered mmap updates and page/block write amplification. HN debated the trade-off between queryable structured logs and append-mostly formats.