Simon,

What is happening is that when we create a preallocated disk on NFS, we fill the file with zeros in order to "allocate" the space.
However, while copying the disk we use qemu-img that will ignore the zeros.

Quick way to demonstrate:

[root@white-vdsd test]# dd if=/dev/zero of=myfile.txt bs=1M count=1
1+0 records in
1+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.00172084 s, 609 MB/s

[root@white-vdsd test]# du -h myfile.txt
1.0M    myfile.txt

[root@white-vdsd test]# ls -lh myfile.txt
-rw-r--r-- 1 root root 1.0M Aug  7 12:39 myfile.txt

[root@white-vdsd test]# qemu-img convert myfile.txt myfile2.txt

[root@white-vdsd test]# ls -lh myfile2.txt
-rw-r--r-- 1 root root 1.0M Aug  7 12:41 myfile2.txt

[root@white-vdsd test]# du -h myfile2.txt
0    myfile2.txt

[root@white-vdsd test]# qemu-img info myfile.txt
image: myfile.txt
file format: raw
virtual size: 1.0M (1048576 bytes)
disk size: 1.0M

[root@white-vdsd test]# qemu-img info myfile2.txt
image: myfile2.txt
file format: raw
virtual size: 1.0M (1048576 bytes)
disk size: 0

I hope this explains what you see.

Regards,
Fred


On Sun, Aug 7, 2016 at 11:13 AM, Simon Barrett <Simon.Barrett@tradingscreen.com> wrote:

Storage is NFS. What logs would you like to see?

Many thanks.

Simon




On Sun, Aug 7, 2016 at 8:53 AM +0100, "Fred Rolland" <frolland@redhat.com> wrote:

Simon hi,

What storage type are you using in source and target storage domains ? (NFS, ISCSI....)

Can you share the logs?

Thanks,
Fred

On Fri, Aug 5, 2016 at 6:37 PM, Simon Barrett <Simon.Barrett@tradingscreen.com> wrote:

Another example. This one was moved to a new storage domain

 

root@ovirt_host1> qemu-img info dd6f25f6-7830-4024-915f-a20268797c34

image: dd6f25f6-7830-4024-915f-a20268797c34

file format: raw

virtual size: 200G (214748364800 bytes)

disk size: 5.0G

 

root@ ovirt_host1> cat dd6f25f6-7830-4024-915f-a20268797c34.meta

DOMAIN=53560d43-874a-49c5-9c5a-8b90487c79f8

VOLTYPE=LEAF

CTIME=1470305678

FORMAT=RAW

IMAGE=741976cd-d1cb-4031-bdbe-6a745dff16ef

DISKTYPE=2

PUUID=00000000-0000-0000-0000-000000000000

LEGALITY=LEGAL

MTIME=0

POOL_UUID=

SIZE=419430400

TYPE=PREALLOCATED

DESCRIPTION=

EOF

 

 

This one has not been moved:

 

root@ny2-lvb-066.mgt> qemu-img info 155f0d33-c280-4236-8d1e-fcb88f9a1242

image: 155f0d33-c280-4236-8d1e-fcb88f9a1242

file format: raw

virtual size: 90G (96636764160 bytes)

disk size: 90G

 

root@ny2-lvb-066.mgt> cat 155f0d33-c280-4236-8d1e-fcb88f9a1242.meta

DOMAIN=59bde2ff-e10d-477e-91c1-6355abff0999

CTIME=1464946639

FORMAT=RAW

DISKTYPE=2

LEGALITY=LEGAL

SIZE=188743680

VOLTYPE=LEAF

DESCRIPTION={"DiskAlias":"ny2-laa-010.prod_Disk1","DiskDescription":""}

IMAGE=82158182-81a4-458e-a41b-663756962666

PUUID=00000000-0000-0000-0000-000000000000

MTIME=0

POOL_UUID=

TYPE=PREALLOCATED

EOF

 

See the mismatch between “virtual size” and “disk size” on the one that was moved.

 

TIA,

 

Simon

 

From: users-bounces@ovirt.org [mailto:users-bounces@ovirt.org] On Behalf Of Simon Barrett
Sent: Friday, 5 August, 2016 10:25
To: users@ovirt.org
Subject: [ovirt-users] preallocated storage issue?

 

If I create a preallocated disk for a VM, I see the disk image file listing as the size I requested (100G):

 

cd /rhev/data-center/mnt/storage_host1:_vol_pa1__nas__01b__oVirt__prod__01/53560d43-874a-49c5-9c5a-8b90487c79f8/images/d97f7706-3662-40bf-9358-80e0dc51bff4

root@ovirt_host> ls -l

total 105064644

-rw-rw---- 1 vdsm kvm 107374182400 Aug  5 10:57 75c14559-e18f-4cc8-a3fe-bc0de507720b

-rw-rw---- 1 vdsm kvm      1048576 Aug  5 10:57 75c14559-e18f-4cc8-a3fe-bc0de507720b.lease

-rw-r--r-- 1 vdsm kvm          313 Aug  5 10:57 75c14559-e18f-4cc8-a3fe-bc0de507720b.meta

 

and the corresponding space used on disk matches

 

root@ ovirt_host > du -sh *

101G    75c14559-e18f-4cc8-a3fe-bc0de507720b

1.1M    75c14559-e18f-4cc8-a3fe-bc0de507720b.lease

4.0K    75c14559-e18f-4cc8-a3fe-bc0de507720b.meta

 

If I then migrate that storage (while the VM is shutdown) to a new storage domain, the size on disk does not match the allocated size. In this case there is nothing in the disk yet so it shows as 0.

 

cd /rhev/data-center/mnt/storage_host2:_vol_pa1__ovirt__uatprod/1f2c2b48-1e77-4c98-a6da-5dc09b78cead/images/d97f7706-3662-40bf-9358-80e0dc51bff4

root@ ovirt_host> ls -l

total 1032

-rw-rw---- 1 vdsm kvm 107374182400 Aug  5 11:06 75c14559-e18f-4cc8-a3fe-bc0de507720b

-rw-rw---- 1 vdsm kvm      1048576 Aug  5 11:06 75c14559-e18f-4cc8-a3fe-bc0de507720b.lease

-rw-r--r-- 1 vdsm kvm          313 Aug  5 11:06 75c14559-e18f-4cc8-a3fe-bc0de507720b.meta

 

root@ ovirt_host > du -sh *

0       75c14559-e18f-4cc8-a3fe-bc0de507720b

1.1M    75c14559-e18f-4cc8-a3fe-bc0de507720b.lease

4.0K    75c14559-e18f-4cc8-a3fe-bc0de507720b.meta

 

oVirt still lists the disk as preallocated in the GUI but it is in fact thin provisioned.

 

I see the same issue if I clone a preallocated VM. The size on disk ends up being the equivalent of a thin-provisioned disk. I also had the issue when importing VM’s from an export domain when I had selected preallocated in the import dialog box.

 

Is this a known issue? Should preallocated not mean preallocated on physical disk?

 

Ovirt Engine is running 3.6.4.1-1.el6

 

The ovirt nodes are running:

 

OS Version:                        RHEL - 7 - 2.1511.el7.centos.2.10

Kernel Version:                 3.10.0 - 327.4.5.el7.x86_64

KVM Version:                    2.3.0 - 31.el7_2.7.1

LIBVIRT Version:               libvirt-1.2.17-13.el7_2.2

VDSM Version:                 vdsm-4.17.23.2-0.el7.centos

SPICE Version:                  0.12.4 - 15.el7

GlusterFS Version:           [N/A]

CEPH Version:                   librbd1-0.80.7-3.el7

 

Many thanks,

 

Simon


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