Comment 7 for bug 1407307
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| Alexei Sheplyakov (asheplyakov) wrote | #7 |
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The reason Fuel documentation recommends to disable QCOW2 format for images is that RBD does not support QCOW2 disks directly, so Nova and Cinder have to convert a QCOW2 image into RAW format before passing
it to QEMU's RBD driver. This means that you end up downloading the QCOW2 image from Ceph to a nova-compute node (first full copy), converting it (second full copy), and uploading the resultant RAW image back to Ceph
(third full copy) just to launch a VM or create a volume from an image.
However copying a 12MB image over the 10Gb link takes ~ 0.01 seconds which is negligible (Linux kernel initialization in a VM takes ~ 1 second)