Questions about Persistence

I had a couple of quick questions about how OpenJMS works in regards to durable subscriptions and message persistence. 

When the JMS provider is storing messages for a durable subscriber that is not alive, where does it store messages?  Is this done to disk, or all kept in memory?

Also, with message persistence, I see that a database can be configured.  However, if it is not configured, does OpenJMS write to disk (some sort of log file) by default?

Looking forward to seeing your responses.

Thanks,

Kulvir