On Wed, 23 Feb 2011, Jonathan Tripathy wrote: > Give that I currently follow the current procedure for removing and adding > customers: > > To remove customer: zero out customer LV, then remove LV > To add customer: create a new LV > > And I want to run backups of a customer's LV using snapshots I just: > create a snapshot of the customer LV, then use rsync, then remove the > snapshot. Is there anything I should do to prevent cross-customer data > leakage? You are still ambiguous. If by "create a new LV", you mean a new LV that is not an LVM snapshot, then just zero it out when you create it (rather than when you delete it). If by "create a new LV", you mean create a new snapshot on a (mostly) readonly origin, then you don't need to do anything. The entire logical volume is (logically) initialized to the origin. There is no need to zero when deleting either. If, in addition to "cross-customer data leakage", you are worried about FBI raids finding old data from deleted customers in LVM free space, then zero independent LVs when deleting (as you planned), and zero *-cow for snapshots before deleting with the origin unmounted (but check with an expert whether that is safe while other snapshots for the same origin are mounted - I think it should be). IDEA - it seems that the device mapper could logically zero an LV by simply returning blocks of zero on reads until the corresponding block it written. Yeah, would require overhead to track which blocks have been written. That overhead could be 1 bit for each of fairly large blocks, and be fairly small, fit into ram easily, and be stored in a logically zeroed block and discarded when the last block is written. So effectively it only requires storing a pointer in meta-data to the current block where the bitmap is stored. I can see that compared to the simplicity of simply writing zeroes on allocation, it might not be worth it. -- Stuart D. Gathman <stuart@bmsi.com> Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154 "Confutatis maledictis, flammis acribus addictis" - background song for a Microsoft sponsored "Where do you want to go from here?" commercial. _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/