I want to run the Kiln Storage Service on a machine that has generally great specs, but insufficient storage. The good news is that I've got an awesome SAN that the box is connected to. Can I store the Mercurial repositories on a SAN?
For the current Windows-only version of the Kiln Storage Service, no.
On Unix systems, Mercurial works properly with NFS-mounted filesystems, and has for some time. If we were to distribute a Unix version of the Kiln Storage Service, mounting a SAN via NFSv4 would be the recommended way for maximum-resilience source code. (This is not quite what we do for Kiln On Demand, but the outcome is the same.)
On Windows, Mercurial is supposed to work properly with CIFS/SMB, but we've encountered enough hard-to-diagnose, non-repeatable corruption issues that we generally don't recommend running things that way. That said, there are, at the present, no known Mercurial bugs when working with a repository on a CIFS/SMB mount, so if you keenly understand the risks, you can go ahead.
In general, the Kiln Storage Service doesn't put that much pressure on RAM or CPU; if you have a machine with a large RAID array, it's best to simply run the Kiln Storage Service on that box.