MD_ASYNC
mdio.md_options |= MD_ASYNC;
mdio.md_options &= ~MD_ASYNC;
if (mdiox.md_options & MD_ASYNC) {
error = VOP_WRITE(vp, &auio, sc->flags & MD_ASYNC ? 0 : IO_SYNC,
sc->flags = mdr->md_options & (MD_ASYNC | MD_CACHE | MD_FORCE |
sc->flags & MD_ASYNC ? 0 : IO_SYNC,