Oracle backup questions...

I'm working on Oracle back-up and recovery, and I've run across a few random questions from looking at what other folks do, and from experimenting on my own.

1. What is the on-disk state of archive logs at arbitrary times? Does Oracle only write them out when they are complete and usable, or does it slowly fill them in over time? Recovering the final archive log here seems to consistently fail, until the next archive log is in place, at which time the one that was previously last is imported without issue.
2. Is there any meaningful difference between "recover database" and "recover database using backup controlfile"?
3. What is "crosscheck archivelog all" as opposed to "crosscheck backup"?
4. How does "delete obsolete" differ from "delete expired backup"?
5. How do we control the frequency of archive log generation? Do I simply say "alter system switch logfile" and wait a bit, or does that only affect redo logs? Should I "alter system archive log all" instead? In short, what should I do to try to bring the archive logs as close to current as is possible?

Thanks very much for your help!

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