The limitation is due to what is supported by the qemu-img snapshot -c command AFAIK this works with qcow only, but perhaps other formats are supported.
use_cow_image=true # always works use_cow_image=false # only works if force_raw_images=false AND original_image_format = qcow Vish On Apr 10, 2012, at 10:42 AM, Lorin Hochstein wrote: > Vish: > > For documentation purposes, if the user wants to be able to do snapshots, > what combinations of the following three variables are allowed? > > 1. original image format (qcow2 | raw) > 2. use_cow_image flag (true | false) > 3. force_raw_images flag (true | false) > > > Take care, > > Lorin > -- > Lorin Hochstein > Lead Architect - Cloud Services > Nimbis Services, Inc. > www.nimbisservices.com > > > > > > On Apr 10, 2012, at 1:32 AM, Vishvananda Ishaya wrote: > >> You can disable using backing files with the following config: >> use_cow_images=false >> >> You should be aware that you likely won't be able to snapshot images unless >> you make sure to upload them all in qcow format and also set: >> force_raw_images=false >> >> On Apr 9, 2012, at 9:37 PM, William Herry wrote: >> >>> 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 >>> >>> [email protected] >>> >>> _______________________________________________ >>> Mailing list: https://launchpad.net/~openstack >>> Post to : [email protected] >>> Unsubscribe : https://launchpad.net/~openstack >>> More help : https://help.launchpad.net/ListHelp >> >> _______________________________________________ >> Mailing list: https://launchpad.net/~openstack >> Post to : [email protected] >> Unsubscribe : https://launchpad.net/~openstack >> More help : https://help.launchpad.net/ListHelp >
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