Mirrored volume sets

I tried to extend a partition on a mirrored drive. The idea was to mirror that extension as well. Sounded good when I first thought it, but it doesn’t seem to work. Can someone tell me if this even possible.

Bearing that in mind, I decided to try a different method. I broke the mirror set, extended the D drive on one of the newer drives, created a volume set with the other two, and tried to mirror the two volume sets.

Obviously I haven’t been able to get that to work or I wouldn’t be posting here.

Any ideas? Original 2 drives where identical in size, the newer 2 was also identical but a couple of mb bigger.

Thanks. (btw- i’m trying to do this with just NT, and not through the use of 3rd party stuff)