Re: [Xen-users] Xen backups using LVM Snapshots

[Mike Lovell <mike@xxxxxxxxxxxx>]

Javier Guerra wrote:
> On Wed, Oct 15, 2008 at 2:17 AM,  <lists@xxxxxxxxxxxxx> wrote:
>   
>> Each DomU with a database has a cron that dumps the db with mysqldump.  
>> Later on, Dom0 will do an LVM Snapshot of all DomUs and then do a file 
>> system backup of the Snapshots.  I do no actions on the DomUs.  No shutdown 
>> or 'xm pause/save/...'
>>     
>
>
> as you must have seen already, those snapshots mount as 'dirty'
> filesystems, since they're exact copies of an already mounted
> filesystem.  therefore, you have to run fsck on mount (usually
> automatic on journalling filesystems).  depending on the journalling
> algorithm, you risk having non-written data.
>   
This isn't sounding quite right to me. According to LVM Howto on
tldp.org a snapshot is "exact copy of a logical volume, frozen at some
point in time." (http://tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html).
>From my experience, creating an LVM snapshot creates a new LVM volume
that stays consistent despite changes on the LVM volume the snapshot was
created from. I'm sure there is a performance decrease since LVM has to
track a lot more information during this time. But it should work. I do
something similar to what is asked about in this and the other email
thread without a problem yet. Here are the tutorials I used for coming
up with the way I do things.

http://tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html
http://howtoforge.com/linux_lvm_snapshots

It seems to work for me.

Mike

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