why does OpenSSH have one big file known_hosts[2] ? 

Newsgroups: comp.security.ssh
> Are there any security risks in having a directory of key files as
> opposed to one big file of key lines?

Doable but it would be 100 files in a directory called known_hosts. Vi the single file and locate the key by name or ip would not be difficult at all. Security wise, single file is also easier to monitor and maintain, as opposed to 200 files (naming convention????? and a security risk as well).