OK. I figured it out in Sept 2015 but forgot to add the solution here... Today we had to do it again and with the help of the Canonical support my memory was jogged. Here's the solution to resizing VMs running under Virsh using LVM's on the Hypervisor..

Firstly increase the Logical Volume: (in this case we are trying to resize the controller VM

sudo lvextend --size +10G /dev/system/controller

After it has resized the LVM to make space for a larger VM disk, we need to use "virt-" commands to rename the current disk to .backup, make new vm disks, and basically copy and expand the data from the old disks onto the new disks.

You can do a

man virt-resize

before you begin.

TO DO : Increase Controller from 10Gb to 20Gb
=====================
virsh shutdown controller
sudo virt-filesystems --long --parts --blkdevs -h -a /dev/system/controller 
sudo lvrename /dev/system/controller /dev/system/controller.backup
sudo lvcreate system -n controller -L 20GB 
sudo virt-resize /dev/system/controller.backup /dev/system/controller --expand /dev/vda1

Then after that

virsh start controller

@hypervisor: ssh maas

from maas

ssh controller

df -h to make sure the controller VM (or whichever VM you were increasing it's size did get it's Filesystem resized)

Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1        20G  8.5G   11G  46% /

Then when you are happy your Openstack is working again Remove the Temporary backups of the FileSystems you made

sudo lvremove /dev/system/controller.backup

NOT the answer but an update:

I read up about virsh blockresize and tried on the VM... http://serverfault.com/questions/604876/online-resizing-of-kvm-guest-root-filesystem (http://serverfault.com/questions/6048...)

@hypervisor:~$ sudo virsh blockresize bootstrap --path /dev/system/bootstrap --size 20G error: Failed to resize block device '/dev/system/bootstrap' error: Requested operation is not valid: domain is not running

PS: this also has the wrong path for the file... /dev/system/bootstrap

so a) sudo virsh start bootstrap b) find the path using ps -faux | grep bootstrap which will show file=/dev/mapper/system-bootstrap

Then:

@hypervisor:~$ sudo virsh blockresize bootstrap --path /dev/mapper/system-bootstrap --size 20G Block device '/dev/mapper/system-bootstrap' is resized

except it doesn't seem to make any difference:

Using fdisk shows (I think similarly to previously after the first lvextend that there is now 21.5Gb hdd avail..) but the OS just wont resize... at this point I wish there was just a way to boot the VM using "gparted live" and resize...

@bootstrap:~$ sudo fdisk -l

Disk /dev/vda: 21.5 GB, 21474836480 bytes 16 heads, 63 sectors/track, 41610 cylinders, total 41943040 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000

Device Boot Start End Blocks Id System /dev/vda1 * 2048 20971519 10484736 83 Linux