[CentOS-virt] Problem with lvm disks assigned to kvm guests

Thu Feb 6 11:05:24 UTC 2014
C. L. Martinez <carlopmart at gmail.com>

On Thu, Feb 6, 2014 at 11:01 AM, Dennis Jacobfeuerborn
<dennisml at conversis.de> wrote:
> On 06.02.2014 11:45, C. L. Martinez wrote:
>> Hi all,
>>   I have a strange problem when I use lvm disks to expose to virtual
>> guests (host is CentOS 6.5 x86_64). If I remove a kvm guest and all
>> lvm disks attached to it, and I create a new kvm with another lvm
>> disks that use the same disk space previously assigned to the previous
>> kvm guest, this new guest sees all partitions and data. Creating new
>> lvm volumes with different names to this new kvm doesn't resolves the
>> problem.
>> Any idea why??
> When you delete a volume the data isn't cleared only the metadata
> removed so if you later create a new volume that ends up using the same
> area on disk then you will see the old data as expected.
> If you don't want this to happen then you need to overwrite the volume
> before you delete it.
> This is a general issue in virtualization/clouds that you need to take
> into account for security reasons. See for example:
> https://github.com/fog/fog/issues/2525
> Regards,
>    Dennis

Many thanks Dennis ... Then if I do:

dd if=/dev/zero of=/dev/sdc1 bs=1M (it is a 1TiB disk), will erase all
data and partitions created by the kvm guest??