Solving the ext3 latency problem

Typically, different services run under different user accounts, and rely on the system's security features to keep the two separate.

It would be bad if a bug in the mail server gave access to, say, deleted .htaccess files, or part of a SQL database.

All Unix systems are inherently multiuser, and sabotaging inter-account security features is deliberately cutting away one layer of the net that can catch you if a bug exposes an attack vector.