[libvirt-users] virt-install creates a snapshot as the volume backend

[Ahmed Ossama]

Thanks Jan.

I upgraded to 0.10.2 again, and specified "sparse=false" and it worked 
perfectly.

On 04/29/2013 06:11 PM, Ján Tomko wrote:
> On 04/28/2013 12:55 AM, Ahmed Ossama wrote:
>> Greetings All,
>>
>> I was running libvirt-0.9.10 on CentOS 6.3 and it was working perfectly until
>> yesterday when I decided to update to 6.4, which upgraded libvirt-0.9.10 to
>> libvirt-0.10.2.
>>
>> I have a storage pool of type volume group, upon upgrading to libvirt-0.10.2,
>> the disk image gets created as a snapshot on the volume group not as a regular
>> volume.
>>
>> Now every time I create a vm using virt-install on a vg, the lv gets created
>> as a snapshot not a regular lv, as a result I get the following error when I
>> run dmesg:
>>
>>      device-mapper: snapshots: Invalidating snapshot: Unable to allocate exception.
>>      Buffer I/O error on device dm-5, logical block 128251
> ...
>> and the following on the domain's log file:
>>
>>      block I/O error in device 'drive-virtio-disk0': Input/output error (5)
>>
>> # virt-install --name="ns1" --vcpus="2" --check-cpu --ram=512
>> --os-variant="rhel6" --network "bridge=br0" --disk
>> "pool=vdisks,size=22,cache=writeback" --vnc --hvm --vnclisten="0.0.0.0"
>> --cdrom="/mnt/ISOs/centos/x86_64/CentOS-6.3-x86_64-bin-DVD1.iso" --hvm
>> # lvs | grep ns
>>    ns1.img          vm_volumes swi-aos--   4.00m      [ns1.img_vorigin]   0.00
>>
>> When I try to create a volume using virt-manager on the volume group, it gets
>> created as a snapshot. But when I create a volume using virsh, it gets created
>> correctly;
>>
>>      virsh # vol-create-as vdisks test 23622320128
>>
>>      # lvs | grep test
>>        test             vm_volumes -wi-a----  22.00g
>>
>> If anyone came across this issue or can provide an advice, I will appreciate
>> it so much.
>>
>> -- 
>> Best Regards,
>> Ahmed Ossama
>>
> Hello,
>
> since 0.10.2 libvirt creates sparse logical volumes when the requested
> allocation is less than requested capacity. Unlike sparse files, these don't
> grow automatically and you get an I/O error if you fill them up. [1]
>
> virt-install requests an allocation of 0, which libvirt interprets as the
> smallest possible value of 4MB. Unfortunately, you can't specify a different
> allocation value at virt-install command line, but a fix that uses the same
> allocation and capacity for logical volumes is committed upstream already [2]
> and should be fixed in next release.
>
> In virt-manager, you should be able to set the allocation to the same value
> manually.
>
> Jan
>
> [1] http://libvirt.org/formatstorage.html#StorageVolFirst
>
> [2] https://git.fedorahosted.org/cgit/virt-manager.git/commit/?id=590c8dbe
> commit 590c8dbebfddb71874de7a98e579264ebae6859f
> Author:     Martin Kletzander <mkletzan at redhat.com>
> AuthorDate: 2013-04-02 13:51:28 +0200
>      Don't support sparse logical volumes
>
>      Sparse logical volumes are supported by libvirt, but only in case the
>      user takes care of the reallocation, which is not what virt-install
>      and virt-manager users want.  This patch defaults the logical volumes
>      to non-sparse ones and makes sure allocation is always equal to
>      capacity for such volumes.
>
>

-- 
Best Regards,
Ahmed Ossama