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storage: add support for QCOW2 cluster_size option

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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@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
This commit is contained in:
Pavel Hrdina
2021-05-12 17:43:36 +02:00
parent 19967f64f4
commit 3e1d2c93a3
10 changed files with 78 additions and 0 deletions
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6
tests/storagevolxml2argvdata/qcow2-clusterSize.argv Normal file
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@@ -0,0 +1,6 @@
qemu-img \
create \
-f qcow2 \
-o compat=0.10,cluster_size=131072 \
/var/lib/libvirt/images/OtherDemo.img \
5242880K