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

["Fajar A. Nugraha" <fajar@xxxxxxxxxxxxx>]

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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