If it's data you care about then you put it in Kafka, unless you're big enough to use something like Cassandra or rich enough to pay a cloud provider to make redundant data storage their problem. Logs are something that you need to write durably and reliably when shit is hitting the fan and your networks are flaking and machines are crashing - so ephemeral disks are out, NFS is out, ad-hoc log collector gossip protocols are out, and anything that relies on single master -> read replica and "promoting" that replica is definitely out.
Kafka is about as lightweight as it gets for anything that can't be single-machine/SPOF. It's a lot simpler and more consistent than any RDBMS. What else would you use? HDFS (or maybe OpenAFS if your ops team is really good) is the only half-reasonable alternative I can think of.
