On 26.05.2018 07:19, tas...@posteo.net wrote:
On 26.05.2018 05:56, fsharpn...@gmail.com wrote:
Ok, I discovered pvs to tell me the disk usage, ran it before and
after cloning a ~10 GB Windows VM, and verified usage was the same
before and after:

$ sudo pvs
  PV         VG         Fmt  Attr PSize  PFree
  /dev/sdb2  qubes_dom0 lvm2 a--  58.76g 8.71g


Actually, the answer is also there in the lvs output. The LSize shows
the upper limit for the volume's size, and the Data% shows how much of
that is used.

When you clone a VM (lets say an appVM), you'll notice another private
volume is created and shows the same figures as the volume it
originates from. But looking at pool00 (the overall container for our
VM volumes), the Data% barely changes if at all.



$ qvm-clone windows windows2
windows2: Cloning private volume
windows2: Cloning root volume

$ sudo pvs
  PV         VG         Fmt  Attr PSize  PFree
  /dev/sdb2  qubes_dom0 lvm2 a--  58.76g 8.71g

Qubes manager gives the disk of the clone VM as 0 before I run it:

https://imgur.com/NGAjTxg

Though afterward it gets the same disk size as the original:

https://imgur.com/hCGUVqs

So again I assume that's the virtual space allocated to the clone
rather than the actual space.

Yes.

The Linux storage options won't show a volume that grows from nothing
and has a size equal to the delta from the parent volume. This is
because the Thin LVM and Btrfs objects are not really hierarchical,
and this can be a good thing because it usually means fewer demands on
you attention... there is less 'care and feeding' necessary with the
Linux options. But you do have to keep an eye on your overall free
space, of course.

If you really need to know the delta size between two related volumes,
there may be a utility out there that scans the volume metadata and
shows you. My guess is you would most likely find it for Btrfs, and it
would be described as a tool related to deduplication (or 'dedup').

And that brings me to another point: On Btrfs if you have two related
files (.img volumes) but suspect they have diverged too much over
time, you can tell Btrfs to perform deduplication to find new
commonalities and reduce the overall space used.

Chris

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