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Merge "Add warning about qcow2 version 2 format images" into stable/xena

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Zuul 2021-09-27 15:36:09 +00:00 committed by Gerrit Code Review
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releasenotes/notes/xena-qcow2-v2-warning-9381189b1c04734f.yaml Normal file
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---
issues:
- |
**NFS-based backend drivers and qcow2 version 2 images**
Under some circumstances, NFS-based backend drivers will store a volume
as a qcow2 image. Thus cinder allows for the possibility that an operator
may choose to manage a storage object in an NFS-based backend that is a
qcow2 image.
Version 3 of the qcow2 format has been the default for qcow2 creation in
qemu-img since QEMU-1.7 (December 2013), and operating system vendors are
discussing discontinuing (or limiting) support of the version 2 format in
upcoming releases.
Thus, we recommend that operators who want to manage a storage object in
an NFS-based storage backend as a cinder volume should not do this with a
qcow2 image that is in the version 2 format, but should change it to the
qcow2-v3 format first.
.. note::
The format version of a qcow2 can be determined by looking for the
``compat`` field in the output of the ``qemu-img info`` command.
A version 2 format image will report ``compat=0.10``, whereas a
qcow2 in version 3 format will report ``compat=1.1``.