Re: [libvirt PATCH 1/2] storage: add support for QCOW2 cluster_size option

The default value hard-coded in QEMU (64KiB) is not always the ideal. Having a possibility to set the cluster_size by user may in specific use-cases improve performance for QCOW2 images. QEMU internally has some limits, the value has to be between 512B and 2048KiB and must by power of two, except when the image has Extended L2 Entries the minimal value has to be 16KiB. Since qemu-img ensures the value is correct and the limit is not always the same libvirt will not duplicate any of these checks as the error message from qemu-img is good enough: Cluster size must be a power of two between 512 and 2048k Resolves: https://gitlab.com/libvirt/libvirt/-/issues/154 Signed-off-by: Pavel Hrdina <phrdina(a)redhat.com&gt; ---

@@ -867,6 +868,11 @@ the file image is used in VM. To create non-raw file images, it requires QEMU version since 2.1. <span class="since">Since 1.2.7</span> </dd> + <dt><code>clusterSize</code></dt> + <dd> Changes the qcow2 cluster size where smaller size can improve image + file size whereas larger size can improve performance. + <span class="since">Since 7.4.0</span>

+ </dd> <dt><code>features</code></dt> <dd>Format-specific features. Only used for <code>qcow2</code> now. Valid sub-elements are:

diff --git a/tests/storagevolxml2xmlin/vol-qcow2-clusterSize.xml b/tests/storagevolxml2xmlin/vol-qcow2-clusterSize.xml new file mode 100644 index 0000000000..22534982a1 --- /dev/null +++ b/tests/storagevolxml2xmlin/vol-qcow2-clusterSize.xml @@ -0,0 +1,17 @@ +<volume> + <name>OtherDemo.img</name> + <key>/var/lib/libvirt/images/OtherDemo.img</key> + <capacity unit="G">5</capacity> + <allocation>294912</allocation> + <target> + <path>/var/lib/libvirt/images/OtherDemo.img</path> + <format type='qcow2'/>

+ <permissions> + <mode>0644</mode> + <owner>0</owner> + <group>0</group> + <label>unconfined_u:object_r:virt_image_t:s0</label> + </permissions> + <clusterSize unit='KiB'>128</clusterSize> + </target> +</volume>