journald by default doesn't keep logs from the previous boot, which is extremely annoying. What's the point of having a logging system where you have to keep the old one around to read old logs? I've also had it seemingly not have any loglines for queried units when it should have; not sure what happened there.
In one configuration, journald logs to an in-memory filesystem; in another, it logs to an on-disc filesystem; in a third, it tries on-disc and falls back to in-memory; in a fourth it does not save the log either in memory or on disc. Different distributions configure this differently.
