How can I know which files a proccess is accessing?

[Eduardo Meyer]

Hello,

I need to know which files under /var a proccess (httpd here) is
acessing. It is not logs because I have a different partition for
logs.

gstat tells me that slice ad0s1h (my /var) is 100% frequently, and in
fact with fstat I can see a number of httpd proccesses running
accesing that. But fstat only shows me inodes and the mount point.

I need to know which files the proccesses are acessing.

How?

Thank you.