Sparse in Virt-clone

[Pankaj Rawat <pankaj.rawat@xxxxxxxxxxx>]

 

Hi all,

 

I am trying to clone a lvm2 image following thing haapens when I clone a image with virt-clone command

 

virt-clone --prompt --force --original  lvm_thin_1 --name  lvm_thin_2 --file /dev/volgrp/lvm_thin2

 

Now when I clone this,  It clone successfully but the cloned image is fully expanded ,  I mean it takes all 100% space

 

#lvs

 

LV	VG	Attr	LSize	Pool Origin	Data%
lvm_thin_1	Volgrp	Vwi-aotz	8.00g	pool	10.18
lvm_thin_2	volgrp	Vwi-a-tz	8.00g	pool	100.00
pool	volgrp	twi-a-tz	100.00g		8.97

                                                                                                                           

 

Now as you can see The 2^nd lvm thin disk is fully expanded to 100%

 

I then downloaded the virtinst source code from the http://virt-manager.org/ site

Package:-  virtinst-0.600.3.tar.gz

 

The I dig into to the code

 

Now  here is what I notice

In file VirtualDisk.py

Function:-    def  _clone_local(self, meter, size_bytes)

 

I changed some code

Here is the diff

 

[root@localhost work]# diff changedcode/virtinst-0.600.3/virtinst/VirtualDisk.py virtinst-0.600.3/virtinst/VirtualDisk.py

1383a1384

>         clone_block_size = 4096

1391a1393

> 

1399c1401

<                     if sparse and zeros == l:

---

>                     if  zeros == l:

1411a1414

> 

 

 

Here I removed the sparse from the condition, and also change the cloned_block_size(varying this value change the cloned image size to some extent)

Initially the sparse is false That’s why the condition is not checked , I skipped that part

 

Now

#lvs

 

LV	VG	Attr	LSize	Pool Origin	Data%
lvm_thin_1	Volgrp	Vwi-aotz	8.00g	pool	10.18
lvm_thin_2	volgrp	Vwi-a-tz	8.00g	pool	8.51
pool	volgrp	twi-a-tz	100.00g		8.97

                                                                                                                           

As you can see clone disk is even more compressed, as all the unnecessary zeros are removed from the source file.

The cloned VM is working file , I double checked it.

 

Now I am not sure whether this is a correct solution for cloning,

 

What I actually want to know is what actually sparse is representing here, why it was initially set to false?

And it what case the sparse condition is actually met?

 

Regards

Pankaj Rawat

 

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