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??