I want to attach a disk to a DomU.
The Xen DomU is running and should not be rebooted. Hence, changing its configuration file is not an option.
How to dynamically attach a disk to running DomU in Xen?
To attach phy:vg_xen/vm-228-large to vm-228 as xvdb, run this on Dom0:
# xl block-attach vm-228 phy:vg_xen/vm-228-large xvdb w
With the old xm tool stack, replace xl with xm.
In the VM vm-228, a new device /dev/xvdb should appear.
The general format for block-attach is as follows.
xl [-v] block-attach <Domain> <BackDev> <FrontDev>
[<Mode>] [BackDomain]
Bonus:
Using this method, you can also mounting a USB drive to a DomU by attaching the whole USB drive (e.g./dev/sde, not the partition /dev/sde1) to a VM as a disk like
# xl block-attach vm-228 /dev/sde xvde w
Note that do not mount the USB drive on Dom0 and umount it if the OS automatically mounted it.
Detach a disk:
# xl block-detach vm-228 xvde
