[linux-lvm] Snapshots and disk re-use
thornber at redhat.com
Wed Feb 23 13:09:33 UTC 2011
On Wed, 2011-02-23 at 12:36 +0000, Jonathan Tripathy wrote:
> Hi Everyone,
> We host many Xen VMs for customers. We use LVM as the fisk storage for
> these VMs. When a customer cancels, we generally dd their LV with
> /dev/zero, before removing the LV.
> If however we want to create a snapshot of a customer's LV, is there the
> chance that the data may appear on a new future LV if we were to create
> one (for a new customer)? Is is my understanding that most filesystems
> don't actually remove data from a disk when deleting a file, but just
> set an "ignore" tag of some sort...
I'm a bit confused about your scenario. But I think this will help:
The snapshot device is composed of 2 sub devices, the origin and the
exception store. Someone who only has visibility of the snapshot (ie.
your vm if your scenario is what I think it is) will have visibility of
all of the origin. So you _do_ need to worry about data leaks on the
origin device. Their view of the exception store is always a subset
which has been overwritten by origin data first. So data leaks are not
an issue for the exception store.
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