the directio attributes is not implemented.
A small patch to have it works :
Index: fileobj.c
===================================================================
RCS file: /cvsroot/filebench/filebench/filebench/fileobj.c,v
retrieving revision 1.44
diff -r1.44 fileobj.c
286a287,291
> #ifdef LINUX_PORT
> if (attrs & FLOW_ATTR_DIRECTIO)
> open_attrs |= O_DIRECT;
> #endif
>
Yes, we encountered the same problem. You actually need to apply your patch at another code path (where the raw device is used). We have fixed this in our locally maintained version: http://www.fsl.cs.sunysb.edu/~vass/filebench/
Fixed in 1.4.9