Root filesystem on LVM on top of Software-Raid1?

[Mark]

Hi,

I have the system root ("/") on a LVM volume that is running on a software raid1 partition (/dev/md0)
I added 2 harddisks and created another raid1 partition on them (/dev/md1).
Now I want to expand the LVM volume over /dev/md1. I did that and my volume shows 18GB, while my filesystem still shows the old size
without the second raid array. I guess I need to use fsck or resize2fs, but the problem is that those tools do not work as long as
the device is mounted.
I can't unmount the filesystem either, because it is the root filesystem.

So I tried booting from the rescue CD, but when the OS comes up in rescue mode, it does not load the raid arrays and lvm volumes.

How can I fix the size of my root partition?

I start thinking it was a bad idea to mount "/" onto an LVM volume over a software-raid? Should I split it out into a regular
partition for "/" and a separate LVM volume on separate partitions and mount that? 

Can I use a software-raid1 array for "/" or will that not be accessable from the rescue CD either?

Thanks,

MARK