Any backup that is not lost due to formatting would mean that it would NOT
be stored physically on your drive. This would mean storing it in some
encrypted form on a public server. But, this is EXACTLY what we want to
avoid. Every system connected to a network is insecure inherently.
Furthermore, if the encyption was done by the server itself, the server
admin has some power over your private key. If it was done by you, you would
have to remember the password / decryption scheme. Where would you store
that?
What you can do, is maintain the private key on an external hard disk, which
you dont format very often. Or go the old age way, of writing it down, and
keeping it in a place secure enough. :). (But most ppl, will disagree with
this writing down business. Leaves too much trail, and there is every chance
of noting down an error.)
--
Pranesh
P.S. - That is the whole point of the private key - it is unbreakable (by
brute force) in real world time. (And there is no way you are going to
remember some digits of that 1024 long string). Security is the prime
issue.