[linux-lvm] LVM snapshot - "dd" file size

[Denie Andriessen]

A compressed dd can still be quite large, as there still might contain non 
zero values..

if you compress the image, a possible way to make the resulting files 
smaller is to:

- do a: 'dd if=/dev/zero of=/dummyfile' on the filesystem first (you might 
want to use 'bs' and 'count' parameters)
- if you topped off the disk, delete the all zero dummyfile.

The zipped result might be smaller. (both with dd and with tar..)

Regards,
Denie

----- Original Message ----- 
From: <dave at frop.net>
To: "LVM general discussion and development" <linux-lvm at redhat.com>
Sent: Wednesday, April 16, 2008 11:04 PM
Subject: Re: [linux-lvm] LVM snapshot - "dd" file size


> this has nothing to do with LVM.
>
> dd knows nothing about files, it just copies the entire device (or file or 
> whatever).
>
> tar will work, if you use the right command line switches. Search around 
> on the web for pointers on how to use it.
>
> Another intermediate way would be to compress the image you get with dd.
>
> On Wed, Apr 16, 2008 at 04:59:05PM +0200, Thomas Bellembois wrote:
>> Hi!
>>
>> I am using LVM partitions on a Debian Xen system.
>> I use LVM snapshots to clone and backup my virtual machines.
>>
>> I have noticed that the ISO file created with the "dd" command it much
>> bigger that the partition used space (actually 4.7GB for the ISO - 500MB
>> used space). No problem if I mount the LVM snapshot and "tar" all of the
>> data.
>>
>> I have googled the question and read that "dd" also copy "not used 
>> space".
>> Why is the ISO file so big ? Is the "tar" method less safe ?
>> Is there a better solution ?
>>
>> Thanks for your answers.
>>
>> Regards,
>>
>> Thomas
>>
>>
>>
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>
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