Windows wont boot after convert from RAW to QCOW2

[Alternativende]

Hello guys,
i have a problem with a Windows 2K08 R2 guest here on Proxmox 5.

I have converted it´s disk from RAW to QCOW2 because the disk is quite large (800GB) and im not even using 230GB of it. Beside this i wanna use snapshots in the near future.

So i have done the conversion with the following command:

qemu-img convert -f raw -O qcow2 vm-100-disk-1.raw /mnt/pve/PVE01-Proxmox/vm-100-disk-1.qcow2

After that i have changed the config of the VM from

bootdisk: sata0
cores: 6
ide2: none,media=cdrom
memory: 10976
name: DC03
net0: e1000=B6:3D:7C:C2:AF:1B,bridge=vmbr0
numa: 0
onboot: 1
ostype: w2k8
sata0: local:100/vm-100-disk-1.raw,cache=writeback,format=raw,size=800G
smbios1: uuid=c79944d1-2027-4753-b350-14b8a5d80148
sockets: 1

to

bootdisk: sata0
cores: 6
ide2: none,media=cdrom
memory: 10976
name: DC03
net0: e1000=B6:3D:7C:C2:AF:1B,bridge=vmbr0
numa: 0
onboot: 1
ostype: w2k8
sata0: local:100/vm-100-disk-1.qcow2,cache=writeback,size=800G
smbios1: uuid=c79944d1-2027-4753-b350-14b8a5d80148
sockets: 1

Both files of course still exist. But when i try to start the machine now Windows complains about important things it can not access and just won´t start.

What did i do wrong here?

Beside the snapshot thing there is another thing because i wanna switch. If this VM is running the disk performance is terrible on the whole server.

Machine turned on, doing nothing:
Timing buffered disk reads: 82 MB in 3.03 seconds = 27.06 MB/sec

Machine turned off:
Timing buffered disk reads: 157.82 MB/sec

 

[kotakomputer]

What was displayed on Console?
Have you try to set "cache=none"?

 

[Alternativende]

I tried it again, now Windows boots into the system recovery mode with the qcow2 disk.

Yes it´s now on NoCache.

Before the migration to qcow2 i ran sdelete -z to free up some space, at that point i didn´t knew that it was a RAW and not a QCOW2. Could that cause a problem?

 

[Alternativende]

So i converted the disk again, same result. I could check it with qemu-img check without any problems. I could also mount the qcow2 file on the host without problems.

But still it runs into system recovery.

Edit:
Just a thought i just had. Could it be that qemu-img changed the size of the disk? The reason i ask is because the RAW file is shown as 801GB big, the QCOW2 file is about 198GB large (which matches with the actual used space in Windows).

Just an idea, im running out of it.