On 6/7/11 4:00 AM, Boniforti Flavio wrote:
> Hello Les and thanks for giving your feedback...
>
> [cut]
>
>> over the whole file.  If they do change and you use rsync,
>> only the differences will be transferred (to the extent that
>> rsync can find them and resync on the matching parts in a
>> huge file), but the server will use the old copy and the
>> differences to reconstruct a full-sized copy which is slow
>> and won't be pooled with anything else.  If the size and rate
>
> So I'm right when thinking that rsync *does* transfer only the bits of a
> file (no matter how big) which have changed, and *not* the whole file?
> It wouldn't matter if I don't get anything pooled, I'd just have to
> choose the correct filesize dimension to store every copy of that VM
> image.

Yes, and you can add the '-C' option to the ssh command in the config to get 
some compressions on the connection.   The transfer will still be slow because 
your server will be reading/uncompressing the old file and copying bits from it 
as it writes the new one.

>> of change makes this impractical, there are some more
>> efficient approaches you could try that would make an
>> intermediate delta-based backup.
>
> Well, size is a critical parameter, because I can suppose that VM images
> are quite *big* files.
> But if the data transfer could be reduced by using rsync (over ssh of
> course), there's no problem because the initial transfer would be done
> by "importing" the VM images from a USB HDD. Therefore, only subsequent
> "backups" (rsyncs) would transfer data.
>
> What do you think?

I don't think backuppc is the best tool for this job but it's not impossible 
for 
it to work.  Whether it is practical or not will depend on the total size and 
rate of change along with your bandwidth and server speed.  One other issue you 
may have to deal with is making sure your backup does not overlap with any 
changes at the local side.  You mentioned that these are already 'copies' but 
if 
they are frequently overwritten you have to be sure that you have gotten a 
consistent snapshot before it changes or it will be unlikely to work when 
restored.  You should also test restoring one so you know what kind of time to 
expect when/if it is needed.

-- 
    Les Mikesell
     lesmikesell AT gmail DOT com

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