Best configuration for "proxy only" squid?

I'm planning to set up a copy of Squid on a backup system so that if some
problem leaves our primary web cache out of service for a protracted period,
we can update the DNS to point at the backup server.

[We cannot assume all clients will be using e.g. Netscape with a suitable
proxy auto-config file, defining fallback to other routes), or that they'll
have set "no-proxy" for the numerous local servers, some of which limit
access to clients in the local domain (at least one client still has proxy
support without a no-proxy option). Hence we need a fallback route which
allows us to ensure direct connection from local clients to local servers,
rather than routing requests direct to a parent cache outside the local
domain.]

The backup system will not have any significant amount of disk space
available for cache (or rather, while it might be possible to give it a
gigabyte or two, it would not be striped wide-SCSI like the primary cache).
There should be adequate memory, though, so that most or all requests could
in theory be handled entirely in-memory. My intention, therefore, was to
try and configure squid as a "pure proxy" (without knowing if it is actually
possible, or if its too firmly ingrained that it's a cache server...).

Trying obvious-seeming things like setting cache_swap to zero and/or setting
cache_stoplist to "." did not seem to stop the objects being written out to
disk and then immediately deleted (I did configure a cache directory
hierarchy - was that the mistake?), assuming the entries SWAPOUT and RELEASE
entries in store.log really do mean that's what has happened.

So ... is it possible to persuade Squid to act as a pure proxy, keeping
objects entirely in memory unless (presumably) that runs short at busy times
(inevitably, when you least want to involve disk I/O...)? If so (and
assuming anyone else has actually tried it!), what is the best combination
of configuration options to set that up?

                                John Line

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