To expand the disk on a XenServer using the command line,   I assume that you have backed up the data elsewhere before the expansion,   as this method deletes everything on the disk to be expanded

• dom0>xe vm-list name-label=<your vm name> # to  get the UUID of the host = VMUUID
• dom0>xe vm-shutdown uuid=<VMUUID>
• dom0>xe vbd-list  params=device,empty,vdi-name-label,vdi-uuid   vm-name-label=<your vm name>  # to get the vdi-uuid of the disk you would like to expand = VDIUUID
• dom0>xe vdi-resize uuid=<VDIUUID> disk-size=120GB #use the size that you would like to expade to
• dom0>xe vm-start uuid=<VMUUID>

Thats it on th dom0,  now as your vm boots up,  log in via SSH and complete the changes by deleting the old partition,  repartitioning and making a new filesystem,   I am going to do this as though the system is mounted at /data

• domU>df /data # to get the device name =DEVICENAME
• domU>umount /dev/DEVICENAME
• domU>fdisk /dev/DEVICENAME
•    [d]  to delete the existing partition
•    [c] to create a new partition
•    [w] to write the partition
•    [q] to close fdisk
• mkfs.ext3 /dev/DEVICENAME
• mount /data
• df /data #to see the file size expanded

Looking for help with XenServer?   Matraex can help.