This is different than my previous thread, and isn't a problem, but more so a question that I hope is do-able.

As like everyone else, I have more storage space than I do RAM. I have BIND set up as a caching name server, and it works as should. But, what I want to do is make it so the caching is saved to disk, instead of RAM.

I know saving data to RAM is done because accessing memory is faster than disk, but I would like to at least have that back up option as right now BIND is running on a VPS that has max 256 MB memory.

Tl;dr: I want to use disk caching instead of RAM caching for BIND.

Bind doesn't really do this, by default, and for good reason. Given that DNS lookups have a very limited time to live, saving lookup results to hard disk, on a server that is rarely rebooted, just slows things down and adds to the load on the server.

Using 'aged-out' lookups is likely to break things - not many things and not at all consistently, so it isn't really a good idea to break networking, however attractive it may appear.

I believe that Pdns can do what you ask for, but whether, when you try it, it turns out to be what you want is another matter entirely. Also note that for a server that is on continuously, there can be no advantage and there are disadvantages.