On 06/04/2011 00:43, Stuart D. Gathman wrote:
In fact, since you still have to zero an LV before removing, you might
as well
zero an LV when you allocate. Same overhead. Then you don't need to
mess
with any of these schemes to deal with snapshots. Did we already cover
that obvious solution? We did discuss a utility to optimize zeroing an
already mostly zero LV.
I think you mean and lv of a virtual machine rather than snap shot, not
sure how you could zero the cow. Stuart does have a good point here,
there is another source of leak outside of snapshots (and probably
worse), if you delete an lv the create a new one over the same PEs the
data from then old lv will be there, save a few k that is zeroed at the
front (to help with fs/label creation). This is worse as it is in order
data that the cow from a snap is not. Geting a while fs back is very
possible.
Try this test
lvcreate -L 256m -n test_lv osiris_l1_vg
yes | dd of=/dev/osiris_l1_vg/test_lv
pvdisplay --map
lvremove /dev/osiris_l1_vg/test_lv
lvcreate -L 256m -n test_lv osiris_l1_vg
pvdisplay --map
od -ha /dev/osiris_l1_vg/test_lv
James
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