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

Thu Feb 6 11:20:37 UTC 2014
C. L. Martinez <carlopmart at gmail.com>

On Thu, Feb 6, 2014 at 11:17 AM, Dennis Jacobfeuerborn
<dennisml at conversis.de> wrote:
> On 06.02.2014 12:05, C. L. Martinez wrote:
>> 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??
> That should work although if you want to be really safe you should
> probably use /dev/urandom instead of /dev/zero as using random data is a
> better way to deal with the problem of data remanence:
> http://en.wikipedia.org/wiki/Data_remanence#Overwriting
> Regards,
>    Dennis

Ok, thanks ... This procedure can works when I reuse a full disk, but
what about if I want to reuse only a logical volume??