[Fedora-xen] Guest Image File Size

[Mark Nielsen]

I think you'll get the same sort of thing if you gzip the file. I've 
gzip'd some 20G xen images down to around 2G.

Daniel P. Berrange wrote:
> On Sat, Dec 01, 2007 at 12:42:40PM -0500, Aaron Metzger wrote:
>   
>> Sadique Puthen wrote:
>>
>>     
>>> Basically it if you don't pre-allocate the entire image, virt-manager 
>>> creates a sparse file to store the guest data which only occupies disk 
>>> blocks while you write contents to that sparse file . When checking the 
>>> size of the pre-allocated and sparse images, you should use "du", not 
>>> "ls -lh".
>>>
>>>       
>> Thank you for your insight.  You are correct.
>>
>> I have a guest image stored in a file called "subversion".
>>
>> "du" shows the actual size being used is smaller than what "ls" thinks.
>>
>> du -a subversion
>> 2158768 subversion
>>
>> ls -ld subversion
>> -rwxr-xr-x 1 root root 64424509441 2007-11-27 18:16 subversion
>>     
>
> You don't need to use  'du' - just use the '-s' flag to ls
>
> $ ls -lsh dan1.img 
> 16K -rwxr-xr-x 1 root root 2.1G 2007-11-29 17:51 dan1.img
>
> Shows its physical size is 16k, while its logical size is 2.1 GB.
>
>   
>> I have a follow up question though.  How do you cleanly backup and 
>> restore these files using the smaller amount of space?  Any simplistic 
>> program that I try (e.g. "tar") also thinks my file is 60 Gig not 2 Gig 
>> and creates a real file that uses 60 Gig of actual disk space.
>>     
>
> Use the --sparse option with tar.
>
>        -S, --sparse
>               handle sparse files efficiently
>
>   
>> Can anyone share the simple steps with "dd" or other programs that let 
>> you cleanly store a backup of the guest image which uses the smaller 
>> amount of space and also correctly restores from that backup in a way 
>> that preserves the orginal idea of a 60 Gig max guest disk size?
>>     
>
> 'cp' will also try to detect sparse files & handle them properly, but
> if it gets it wrong you can also use  '--sparse=always'
>
> Dan
>