mounting RHEL boot disk under Ubuntu

[Rick Cochran <]

I tried moving the boot disk from an old RHEL box to a new Ubuntu box.  Mount 
said that it didn't recognize any filesystems.

I discovered that Ubuntu doesn't install or use lvm by default.  RHEL uses lvm. 
 I installed lvm on the Ubuntu box.  I also installed evms-gui.  It could see 
the logical volumes on the RHEL disk, but I still couldn't mount them.

I rebooted to see if that would make any difference.  It did - Ubuntu dropped 
into BusyBox.  :-(

I removed the RHEL disk, and Ubuntu boots properly now.

Two questions:

What happened?

How can I regain the use of (if not the data from [which I backed up painfully 
but successfully in advance thank God]) the RHEL disk?

-Rick