Hi,
Not able to say for sure on this but I suspect that this is still correct. I have worked with smartarrays on Alpha systems [5300 series] and you can only go DOWN with raid levels and not up.
When you do this, say going down from Raid1 to raid0, then you would be freeing up the mirrored blocks [50% of what is there] for use as spare capacity in the array. You can then use this "spare" capacity to create a new drive.
Therefore, it would not be possible to migrate from Raid0 to Raid1 as all the blocks are allocated already. There is nothing to free up in the first place. Even if you think that "I've only used 25% of the capacity for real data" it dosn't matter as all the blocks are in use for your Raid0 drive.
There may be a "trick" or someone else may have a solution / know better but I suspect it would be as the other noter has said, backup, delete Raid0, recreate Raid1, restore data.
Mark...
if you have nothing useful to say, say nothing...