Re: [Xen-users] what to backup Xen partition with?

[Nico Kadel-Garcia <nkadel@xxxxxxxxx>]

JHJE (Jan Holst Jensen) wrote:
> > I have 4 x 10GB to backup. Of course, the backup is done 
> > while the domains are down.
> > The domains are 4 different Linux distributions I make tests on.
> >     
> [...]
>   
> > But it's still too slow (dd+bzip2). Would you know another 
> > way to make partition backups?
> >     
> Hi.
>
> Since these are all Linux distros, AND you are backing up while the
> domains are down, I would suggest that you simply mount the partitions
> and do a tarball of the file system - or do an rsync of the whole thing
> for even better performance.
>   
dd will always be slow and oversized! You have to read every single 
byte, and if you're writing to a file on the same disk, the disk is 
going to be chugging back and forth even worse. Even on another disk, 
it's hardly efficient. And if it's a live file system, you're in danger 
because it's possible, even likely that blocks will not yet be written 
to disk and you can have an extremely corrupt filesystem recorded 
without the information to fix it.
So don't do partition backups. Store a note about the size and location 
of the partition, a note about the type of file system, then mount it 
and do a tarball of the files. There are techniques to make a 
file-system snapshot and a "paused" copy of the Xen domain that may also 
help: snapshot it and build a new domaiun frm the copy, then shut the 
copy down and make a tarball from *that*. It'll also restore to a new 
partition a lot faster than a dd copy, and you can use a different sized 
partition for the newly restored domain if desired.
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