[CentOS] Expanding EVMS raid1 array

I started with two 160GB drives in RAID1 using EVMS on Centos 4.4.
Both drives have now been replaced with 320GB drives but naturally are
only offering 160GB (they were replaced individually at different
times and self-recovered as they were RAID1. 

I cannot work out how to increase the size of the array to use all the
available space on the disk.

If I understand correctly, I should unmount the array, deactivate it
and select expand. The problem is that while I can unmount and
deactivate it, there is nothing to expand (selecting expand volume,
expand storage object and expand container all report no items found).
Also, right clicking on the array (in EVMSGUI) doesn't have expand as
an option.

The disks are formatted in Ext2/3.

Have I missed something? 

I'd rather not replace the old drives, create a second RAID array and
copy all the data across as I've a feeling that I'll then have to
reset permissions and shares (although I just might get away with then
removing the original RAID array and mounting the new one in the same
location). In my mind it also ought to be easier to simply re-size the
array than have to set up new ones and move the data across.
--

Peter Crighton