Re: AW: [Xen-users] snapshot - backup for xen vm's

[Xin Chen <xcheney@xxxxxxxxxxxxxx>]

Fajar A. Nugraha wrote:

> Xin Chen wrote:
>  
>
> > idea 2: given by Fajar, correct me if I misunderstand.
> >
> > 1), assume I put all guest images in dom 0   /var/lib/xen/images      
> > (image1, image2 ...) each image is a guest system.
> > 2), make snapshot for /var/lib/xen/images.    question: if image1 is
> > 10G, image2 is 20G, how large the snapshot needs? 30G enough? I am
> > quit sure how snapshot works when it is a very big image file.
> >    
> For LVM snapshots, you have to allocate enough space to accomodate
> CHANGES only. For example :
> - if you have 30G total of data (in this case disk image) to backup
> - backup process is estimated to take 1 hour
> - in that 1 hour, it is estimated that would be 5 GB changes
>
> then you only need to allocate 5GB or so for the snapshot. The command
> "lvs" will show you how much space is used for snapshot. You need to
> make sure that the snapshot isn't 100% full. Example :
>
> # lvs
>  LV              VG     Attr   LSize  Origin Snap%  Move Log Copy%
>  rootlv          rootvg owi-ao 10.00G
>  rootsnaplv      rootvg swi-ao  1.00G rootlv   0.06
>
> In this case the original filesystem is 10GB, and I allocate 1 GB for
> the snapshot, from which only
> 0.06 is used.
>
>  
>
> > 3), mount snapshot
> > 4), copy image1 .... copy image2.......
> > 5), umount
> > 6), remove snapshot.
> > question: the image1.bak actually is a backup of a running guest
> > system, when I start the system by this image1.bak, the system is
> > gonna be OK? It is like a reboot a running system, isn't it?
> >    
> Exactly. To be more specific, it will be like if you run "reboot -f", or
> a reboot in the event of power failure. There will be some automatic
> log-replay (if you use journaling filesystem), but if your system can
> survive a power failure then it can survive the snapshot-backup-restore.
>
>  
Hi Fajar,

Thanks a lot for making this clear! In this case, the snapshot is still 
on risk of rebooting issue.
So idea 1(save/restore) is safer but has system down time.
idea 2 is 24 hours running but on a rebooting risk.
Isn't there a better idea of backing up xen guest images? what about the 
live-imigration? Can we use that?
All comments welcome.
x

> Regards,
>
> Fajar
>  



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