[Xen-users] Re: Mounting domU filesystem on Dom0. (xm mount)

[Ligesh <myself@xxxxxxxxxx>]

On Thu, Mar 15, 2007 at 11:49:13AM +0200, Siim Vahtre wrote:
> On Thu, 15 Mar 2007, Ligesh wrote:
> 
> >In fact, that's a nice way to do perfect backup. Take an lvm snapshot 
> >and also save the ram image, and you can restore the state perfectly.
> 
> Don't forget that you need to get memory and LVM snapshots in the _exact_ 
> time. But if you "xm pause" just before snapshot+save, it might actually 
> work (I really don't know).

 Save will automatically pause it. 

 xm save <dom> filename
 lvm snapshot
 xm restore filename
 backup filename + snapshot

 
 [quote] 
> 
> However, you won't have "perfect" state. You will, for example, probably 
> have a nice mess with your network connections if you restore the ram 
> image after some connections have already timed out. It _might_ be a 
> problem.
> 
[/quote] 

 I don't think that's an issue, since it is used in live migration. It would be 
equivalent to a very delayed live migration. The kernel as such is a non-real 
time system, so as far as the kernel is concerned, it would equivalent to other 
end forcibly closing the connection. Everything will always be in a wait state 
in the kernel--except for the single active thread, so when the kernel takes 
the networking part from the wait queue and runs it, it will just find that the 
other end has closed in the period it was in wait, and I don't think this is 
too different from what happens in a normal system.




> >lvm2 snapshot
> >e2fsck -f -y /dev/lvm-snapshot
> >mount -o ro /dev/lvm-snapshot /mnt/backup
> >rsync /mnt/backup
> 
> You don't need forced fsck. Journal reply should be enough. But occational 
> full fsck might be useful nevertheless.

 Will a mount automatically recover the journal?

 Thanks.



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