Comment 7 for bug 1407307
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| Alexei Sheplyakov (asheplyakov) wrote | #7 |
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0f7b58d
(Get the code!)
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)