Thanks for all responses which solved my problem!

My main problem was using the raid raw partition '/dev/raid0d' (i386)
for mounting: That disabled the raidctl control access.

Second, I was not aware of the fact that running 'raidctl -i ...'
doesn't destroy the data on an already built raid and is the solution
for my crash damaged raid1 (though it was mentioned in the raidctl man
page ;-)).

    Greg> [Thanks for waiting until I was back from holidays before
    Greg> asking your question ;) ]

Yep, sometimes murphies law helps... ;-)

    Greg> In -current as of today, you can do that by simply running
    Greg> raidctl in the background (as someone else suggested). I've
    Greg> got changes waiting to go in (perhaps tonight) that will
    Greg> have the check done in the background by default... (there
    Greg> are some new raidctl options and what-not too...) In any
    Greg> case, it's all coming *very* soon to a -current machine near
    Greg> you :)

Great! Will this go into NetBSD 1.4.2, too?

Markus.