WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] live saving of domU

To: "Anthony Liguori" <aliguori@xxxxxxxxxx>
Subject: Re: [Xen-devel] live saving of domU
From: "Jayesh Salvi" <jayeshsalvi@xxxxxxxxx>
Date: Wed, 10 May 2006 14:06:24 -0500
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ewan Mellor <ewan@xxxxxxxxxxxxx>
Delivery-date: Wed, 10 May 2006 12:06:45 -0700
Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:references; b=TjgiF6ses2TWVW4QgqlnKaHTo8cSIW6t2Uh+rjjMqvu74HHQkP6mlivEhmVr3GoZOaVQbioZsSxBnxmnX6iPFoAC9ou56IplmiZyy/DBxGNfNhSJo33Li6YwzHPDs5+lwIyb9WImOiZstPOuYdgdqosC2CbT40FYVJlxWo+40aI=
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <44621BDD.9060401@xxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <871640aa0605100840t14a9f9deqf5c9be99f56917b7@xxxxxxxxxxxxxx> <20060510163213.GF4954@xxxxxxxxxxxxxxxxxxxxxx> <44621BDD.9060401@xxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx


On 5/10/06, Anthony Liguori <aliguori@xxxxxxxxxx> wrote:
Ewan Mellor wrote:
> On Wed, May 10, 2006 at 10:40:31AM -0500, Jayesh Salvi wrote:
>
>
>> Hi,
>>
>> Could anyone tell me, why 'xm save' has live parameter set to false by
>> default. From yesterday's patch ([PATCH] [XenD] Migration-related change)
>> i guess this paramter is renamed to network.
>>
>
> This parameter has not been renamed -- the rename was for a similar flag
> passed in to the device migration code, but the live flag for migration
> remains.
>
>
>> [Snip]
>>
>> I am interested in saving the state of a virtual machine to a file, but
>> want to continue it running. I want to backup the state of the machine, so
>> I want this to be unintrusive operation. I would like to pause the domU
>> and save it to file but keeping it still in memory. After save to file is
>> done I will unpause the domU.
>>
>> I don't see why this shouldn't be possible if live migration works so
>> well.
>>
>
> The reason it's not supported at the moment is this: if you take a snapshot of
> a VM, then run for a bit, and then try and run the snapshot against the same
> filesystem that you were using before, you will inevitably corrupt the
> filesystem.
>

Moreover, you cannot dump the state of a domain after a pause and expect
it to ever run again.

Guests are aware of the physical addresses of the memory that's been
allocated to them.  Because of this, to save a domain's state in a
restorable way you need the guest to "canonicalize" itself.  The only
way to do this today is through a suspend operation which happens to be
a subop of shutdown.  Shutdowns are non-recoverable so you cannot use
this as a snapshotting mechanism.

Thanks, that was informative. But the shutdown you are refering to here is not the traditional shutdown of domU right? I mean 'xm shutdown' will do proper shutdown of domU OS, the shutdown you are referring while doing 'xm save' is different from that, I hope!

The closest thing you can achieve is a localhost migration.  There are
some caveats to this, of course.  The first is that you need to have as
much memory as the domain has available since you'll have a copy of the
domain created briefly while the migration takes place.  Migrations are
also quite intrusive since they involve tearing down and bringing up all
the devices.

I've gotten a lot of requests for light weight checkpointing.  AFAIK,
noone is actually working on it though.
Regards,

Anthony Liguori

> If you had a way to snapshot the storage at the same time as the VM, then you
> could make live snapshotting of VMs work properly.  As it is, this is not
> integrated into Xend at the moment, and not supported because of the danger of
> filesystem corruption if you don't know what you are doing.
>
> Ewan.
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
>




--
Jayesh
------------------------------------------------------------------------
Everything you can imagine is real
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel