Firewall high availability Strategy

[David Cragg <david @ ilanet . slnsw . gov . au>]

I am wondering what strategies people have in place incase their
firewalls go bung (eg. a disk crash). Our main priority here is to 
minimise downtime. I am looking at a number of options, but
they either impact performance or cost heaps (eg mirroring
and redundant firewalls).

I am wondering what is the most popular method other people
use to keep their firewalls up and going in the event of 
disasters.

Regards,

David Cragg