I saw a question online that I thought would be good to answer:
If I have an existing file server for our office, and want to keep a spare server ready to go how can I implement this?
The question actually is about cross platform Linux -> Vista backup, but I'll broaden the question a little to cover how to do this regardless of if your current server is Solaris, Linux, Samba, or Windows.
There is a free tool called rsync which can sync remote files across systems. It's cross platform, so we don't need to be concerned what platform the source or destination servers are, i.e. they can be Linux, Solaris, Windows, or any other supported platform. So this tool allows us to handle the "copy". Rsync also is very effecient at sending changes only and not recopying identical files, so it can be run often to keep your "hot spare" relatively up to date.
The next step is having the "shares" set up on the "hot spare" server, for this I do *NOT* recommend just leaving shares there configured - That gives a possibility for users to access the files on the wrong share, since you are simply overwriting anything "out of sync" the changes would be overwritten from the older file, causing data to be missing.
Instead I recommend set up the shares, but set the permissions on the shares such that nobody can access them. Another advantage to this is if you happen to be out of the office when they need to fail over then I feel it's MUCH SIMPLER to explain setting permissions than setting up the shares + permissions.
CAUTION: Your file permissions are not going to copy cross platform, so you want to be cautious of this. However many small offices don't use any complex permissions anyway.
NOTE: This solution is a "no budget" solution, you shouldn't use it except for a very small office that truly can't afford a spare server. In reality you want a TRUE spare server with real time replication - the simplest config that I'd recommend is using DFS between two windows servers.