[pve-devel] Sparse clone/move over a thin LVM ?

Gilles Pietri contact+dev at gilouweb.com
Thu Jul 28 01:12:30 CEST 2016


Hi,

If I clone or move a disk (coldly, vm stopped), the disk is copied using
qemu-img convert, if I'm not mistaken. For some reasons, even though
qemu-img supports sparse creation, copying from a thin LVM to another
one, or from a QCOW2 to a thin LVM, the destination file is always fully
zeroed. Which renders the lvm thin rather useless.

So I tried it by hand using dd conv=sparse, which works fine...
I'm no expert at this, but could it be that we could move/clone
sparse/thin disks this way if the destination is indeed a newly created
LV (case for move/clone) ?

The reason for the limited scope is that I guess it would be problematic
if we didn't zero already existing blocks on a LV...

Cheers,

Gilles


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