Have you specifically identified this as a problem for your application? I'm curious about this behavior if you have, including the technical details of the disks you are using. Can you elaborate?

If the amount of time that it takes you to get something off a disk is very large compared to whatever you are doing, something seems odd.

If that is really a problem though, you might want to look into a design that knows to buffer lines from the file, and to get more lines when it runs low. You're still paying the penalty for reading lines though. Something like sysread might give you a little boost, but then you have to spend time figuring out whre the line breaks are.