I'm having the exact same problem. Check out the thread starting with
<http://lists.debian.org/debian-sparc/2004/debian-sparc-200402/msg00077.html>.
booting with nodma has made my ide subsystem completely stable,
including an md raid1 mirror pair. I'm still trying to get the bug
workaround described in that thread working, but my source has been
out of town, so I'm stalled for now.
Marc