[virt-tools-list] Sparse in Virt-clone

[Pankaj Rawat]

To Simplify the things I am adding the code snippet of the unchanged code.



File:-                      VirtualDisk.py

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





        zeros = '\0' * 4096



        src_fd, dst_fd = None, None

        try:

            try:

                src_fd = os.open(self.clone_path, os.O_RDONLY)

                dst_fd = os.open(self.path, os.O_WRONLY | os.O_CREAT)



                i = 0

                while 1:

                    l = os.read(src_fd, clone_block_size)

                    s = len(l)

                    if s == 0:

                        meter.end(size_bytes)

                        break

                    # check sequence of zeros

                    if sparse and zeros == l:                                                                            # here sparse is false , I tried many option

                        os.lseek(dst_fd, s, 1)

                    else:

                        b = os.write(dst_fd, l)

                        if s != b:

                            meter.end(i)

                            break





Now in above code the sparse is always false , I don't know why ? I tried many options. Because of this the code never go in if statement and always else part gets executed  as a result os.write() function call always get executed, hence the guest VM expand to full size. Can anyone  tell me why this sparse option always false? How can we make it true?



-----Original Message-----
From: Pankaj Rawat
Sent: 12 September 2012 15:43
To: 'Richard W.M. Jones'
Cc: 'virt-tools-list at redhat.com'
Subject: RE: [virt-tools-list] Sparse in Virt-clone



Hi Richard,

Thanks for the input,



I have mentioned In my previous mail the code snippet which is affecting the size of the cloned image, But I am not sure if this is the correct way to do this.



I managed to get a fully working cloned VM (from virt-clone) with size even less than the original one . That is the reason I am confused about this Code change.



And I also want to know why sparse in VolumeDisk.py  code snippet mentioned in my previous mail is initially FALSE



Regards,

Pankaj Rawat

NECHCL ST







-----Original Message-----

From: Richard W.M. Jones [mailto:rjones at redhat.com]

Sent: 12 September 2012 15:16

To: Pankaj Rawat

Cc: 'virt-tools-list at redhat.com'

Subject: Re: [virt-tools-list] Sparse in Virt-clone





On Wed, Sep 12, 2012 at 07:28:46AM +0000, Pankaj Rawat wrote:

>

> 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



virt-clone doesn't give you much value here.  It basically makes a few changes to the libvirt XML configuration (like assigning a new name and UUID) which you could easily do yourself.



So the real question is how to copy a thin-provisioned LV and keep it sparse.  I don't see a way to do this, but you could create a snapshot of the original using the regular tools (lvcreate).



Rich.



--

Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones New in Fedora 11: Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 70 libraries supprt'd http://fedoraproject.org/wiki/MinGW http://www.annexia.org/fedora_mingw




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