Hi Redhat Team,
Thanks for the information on QCOW2
On ISCSI storage domain, if am creating a floating disk with “raw” + “sparse”.
Then it gives me an error that this is not a valid format for this storage
domain type.
<disk>
<storage_domains>
<storage_domain id="834df3ca-b9c2-45d3-ade9-6384dc1517da"/>
</storage_domains>
<name>mydisk</name>
<provisioned_size>400</provisioned_size>
<format>raw</format>
<sparse>true</sparse>
</disk>
Response
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<fault>
<detail>[Cannot add Virtual Disk. Disk configuration (RAW Sparse) is
incompatible with the storage domain type.]</detail>
<reason>Operation Failed</reason>
</fault>
On further digging I found a already opened BZ for it
https://bugzilla.redhat.com/show_bug.cgi?id=1600547
Is this going to be fixed in the near future ?
Right now, it creates only COW disk if thin provisioning is chosen.
From: Nir Soffer <[email protected]>
Date: Thursday, November 15, 2018 at 10:25 PM
To: devel <[email protected]>
Cc: Suchitra Herwadkar <[email protected]>, Mahesh Falmari
<[email protected]>, Daniel Erez <[email protected]>, "Nisan, Tal"
<[email protected]>, Pavan Chavva <[email protected]>, Raj Asher
<[email protected]>, Himani Vaidya <[email protected]>
Subject: [EXTERNAL] [BACKUP] Estimating qcow2 disk image size before upload
When uploading to qcow2 disks on block storage you must set the disk
initial_size
correctly so the system allocates big enough disk. If the initial size is too
small, the
upload will fail when trying to write after the end of the device.
This info can be useful for people working on a backup solution for oVirt.
The easiest case is upload of existing qcow2 image using the SDK. In this case
we
create a new disk with:
initial_size=image_size,
provisioned_size=virtual_size,
image_size is the size of the file:
os.stat('image').st_size
Note that "qemu-img info" return "actual-size" - this is the allocated size on
storage
which is not helpful for uploading images.
Example:
https://github.com/oVirt/ovirt-engine-sdk/blob/78c3d5bd14eeb93ef72ec31d775ff5c41f51a8c7/sdk/examples/upload_disk.py#L123
A more tricky case is when a backup system keeps raw guest data, but know how
to generate qcow2 image stream, without creating a temporary image.
In this case the required size can be calculated by counting the number of
clusters that need to be allocated in the final image. This depends on the
location of the data in the image.
For example this creates 1G image with only one cluster:
$ python -c 'with open("one-cluster.raw", "wb") as f:
f.truncate(1024**3)
f.write("x")'
$ ls -lhs one-cluster.raw
4.0K -rw-rw-r--. 1 nsoffer nsoffer 1.0G Nov 15 18:24 one-cluster.raw
$ qemu-img measure -f raw -O qcow2 one-cluster.raw
required size: 458752
fully allocated size: 1074135040
$ qemu-img convert -f raw -O qcow2 one-cluster.raw one-cluster.qcow2
$ ls -lhs one-cluster.qcow2
324K -rw-r--r--. 1 nsoffer nsoffer 384K Nov 15 18:25 one-cluster.qcow2
But this creates a fully allocated 1G image:
$ python -c 'with open("fully-allocated.raw", "wb") as f:
f.truncate(1024**3)
for i in range(0, 1024**3, 64 * 1024):
f.seek(i)
f.write("x")'
$ ls -lhs fully-allocated.raw
64M -rw-rw-r--. 1 nsoffer nsoffer 1.0G Nov 15 18:30 fully-allocated.raw
$ qemu-img measure -f raw -O qcow2 fully-allocated.raw
required size: 1074135040
fully allocated size: 1074135040
$ qemu-img convert -f raw -O qcow2 fully-allocated.raw fully-allocated.qcow2
$ ls -lhs fully-allocated.qcow2
1.1G -rw-r--r--. 1 nsoffer nsoffer 1.1G Nov 15 18:31 fully-allocated.qcow2
We had code in vdsm that does exactly this, and it was removed since qemu-img
support a new "measure" command in RHEL 7.5 providing this info. But this works
only for existing images.
You can find the code in this vdsm commit:
https://github.com/oVirt/vdsm/tree/4eee97d6aa532b6f3ecdfde0333d17c27c412f86
The module implementing estimation:
https://github.com/oVirt/vdsm/blob/4eee97d6aa532b6f3ecdfde0333d17c27c412f86/lib/vdsm/storage/qcow2.py
The tests for this module:
https://github.com/oVirt/vdsm/blob/4eee97d6aa532b6f3ecdfde0333d17c27c412f86/tests/storage/qcow2_test.py
If you know the data ranges that will be written to the qcow2 image, you can
count
the clusters like this:
https://github.com/oVirt/vdsm/blob/4eee97d6aa532b6f3ecdfde0333d17c27c412f86/lib/vdsm/storage/qcow2.py#L168
Then you can use the cluster count to estimate qcow2 file size:
https://github.com/oVirt/vdsm/blob/4eee97d6aa532b6f3ecdfde0333d17c27c412f86/lib/vdsm/storage/qcow2.py#L147
Nir
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