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

[Xin Chen <xcheney@xxxxxxxxxxxxxx>]

Thanks a lot! It really helps.

Let me summarise some backup ideas here: (only for file-backed image Dom U)

Dom 0: LVM
Dom U: file-backed image,  LVM inside Dom U.

Backup dom U:

idea 1:  given by Petersson Mats

# xm save domU somefile
# cp domU.img domU.img.bak
# cp somefile somefile.bak
# xm restore somefile

note: save / restore for full-virtual is only available in Xen 3.10.

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.
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? correct me. plz. or 
maybe some reference for my stupid question.
---
compare: idea 1 seems easier to do, but the system would be unavailable 
for 10 or more mins, copy 10G file isn't so quick.....
idea 2 seems more complicate, but it make the system running 24 hours.

Is there any better ideas for backing up xen guest file based dom U ? 
please advise.
Thanks a lot for all kind people in the xen-list.

cheers,
x




Fajar A. Nugraha wrote:

> Xin Chen wrote:
>  
>
> > Does this snapshot backup idea work with image?
> >
> > I didn't put guest system as partition, I put them as image, one huge
> > image. Does this backup way work with image?
> >
> >    
> "backup from vm with mounting an archive nfs-server", like Josef did,
> works pretty much for any kind of setup since you're doing backups from
> domU (not 0). But in that case you don't create a snapshot first.
>
> An example whre this might be good, is if you only have small files
> which rarely changed (think php web pages, config files, etc.).
>
> An example where this might be BAD :
> - You have mysql or oracle
> - Store data on LARGE datafiles (say several hundred MBs)
> - Your database server is busy, accessed and updated all the time
> - You "backup" the datafile by copying it to remote nfs server while the
> db server is running
> Which leads to unrecoverable, inconsistent database.
>
> My initial suggestion to Josef's question was to use LVMs for domU
> storage, and use LVM snapshot to create a "consistent" view of the
> filesystem at that time.
>
> If you use file-backed image domU, stored on domU filesystem, then you
> can still use LVM snapshots. It just requires a few different steps.
> Assuming your dom0 is stored on LVM (not partition):
> - create an LVM snapshot of dom0's fileystem
> - mount that snapshot
> - backup your image from that snapshot
>
> Note that in this case you backup the entire domU HD image, and NOT
> their content. If your domU uses LVM setup (inside the domU), then this
> is pretty much the only option you have. You can backup the disk image,
> but not the content directly.
>
> However,
> If you use those file-based disk images as direct partitions on domU,
> you can mount the file from that snapshot to get their content.
> If your domU use partition setup (not LVM setup), you can use kpartx and
> create block device entries.
>
>  
>
> > cause I don't wanna to save /restore everytime when I backup the guest
> > system. It takes 10 mins downtime!
> >
> >    
> You don't have to. Not if you just want to backup the disk image or its
> content.
> Regards,
>
> Fajar
>
>
>  
>
> > cheers!
> >
> > it-news (Josef Lahmer) wrote:
> >
> >    
> >
> > > dear ralf schenk,
> > > dear Fajar,
> > >
> > > i've useing the xensource installation iso which does lvm on dom0 by
> > > default and i am quite happy with this installation.
> > >
> > > now i'm using backup from vm with mounting an archive nfs-server
> > > store and copy the important files.
> > >
> > >      
>
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>  

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