Open Stack

Hi

I read from an article that said use preallocation can improve disk I/O
performance in kvm, when I add it to openstack, suck error come to me

(nova.rpc.amqp): TRACE: Stderr: 'Backing file and preallocation cannot be
used at the same time\nqemu-img:
/usr/local/lib/python2.7/dist-packages/nova-2012.1-py2.7.egg/instances/instance-0000000e/disk:
error while creating qcow2: Invalid argument\n'

I was added it to utils.py in virt/libvirt directory (line 77)

def create_cow_image(backing_file, path):
    """Create COW image

    Creates a COW image with the given backing file

    :param backing_file: Existing image on which to base the COW image
    :param path: Desired location of the COW image
    """
    execute(FLAGS.qemu_img, 'create', '-f', 'qcow2', '-o',
             'preallocation=metadata,cluster_size=2M,backing_file=%s' %
              backing_file, path)

here is the article:
http://itscblog.tamu.edu/improve-disk-io-performance-in-kvm/

so what is Backing file for, can I disable it for use preallocation cause I
can't got both

Thanks

-- 

===========================
William Herry

WilliamHerryChina at Gmail.com
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