Linux buffer cache monitoring

I know this is a bit off-topic for an Oracle list, but I know lots of you are running Oracle on Linux so you might know the answer to this.  

I'm doing some I/O capacity testing with Orion on a new server running Oracle Enterprise Linux 5, and I can't figure out how to tell how much of my I/O is being satisfied by the Linux filesystem buffer cache and how much is actually going to disk. In HPUX and AIX, I know I can run "sar -b" to get this information, but that command doesn't provide the same info in Linux (at least not on this version of Linux). I've tried looking through the man pages for sar, iostat and vmstat, and all over the Internet and I can't find the answer anywhere so I'd really appreciate it if anyone can point me in the right direction.  

Thanks!

Brandon  

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