In message <200001281833.KAA01010@lestat.nas.nasa.gov>, Jason Thorpe writes:
>The problem is that the tunefs's change of the superblock was undone
>by the file system writing its copy of the superblock back out to disk.

I found a workaround.

	# kill 1
	[...]
	Enter pathname[...]
	# sync
	# sync
	# tunefs -A -n enable /dev/rwd0a
	# [hit power switch]

-s