"drive reset/restore failed" messages - how to fix?

[Grant Collins]

I have a disk which has suddenly started reporting errors like so:

xd0a: read retry (operation timeout) -- blk #192, abs blk #192
xd0a: write retry (operation timeout) -- blk #192, abs blk #192
xd0a: read failed (operation timeout) -- blk #-774978, abs blk #192
xd0a: write retry (operation timeout) -- blk #192, abs blk #192
xd0a: read restore (drive seek error) -- blk #192, abs blk #192
xd0a: write restore (drive seek error) -- blk #192, abs blk #192
xd0a: drive reset failed (operation timeout) -- blk #0, abs blk #0
xd0a: drive reset restore (disk seek error) -- blk #0, abs blk #0
xd0a: drive reset retry (operation timeout) -- blk #192, abs blk #192

These errors are being reported on both the root and /usr partitions (bummer).
Sun reckons I should reformat the drive, installboot, newfs & restore - it
all seems a bit drastic.  Has anyone come across this before and if so, is
there an easier solution to the problem?  What causes it??
Any help much appreciated..
Regards,
gbc.

p.s. Machine is a Sun 4/200 series running SunOS 4.0.3, Xylogics controller,
2*688Mb SMD disks  (if that helps).