Xen users - Apr 2010 - Online resize of guest disks without reboot/shutdown ?

Hello all,

I just notice the new feature in the latest version 4 release.

Any one know how to do this ?

I have tried lvextend the partition size in dom0,
but domU doesn''t see the change.
I also need to reboot to make domU reread the block size.

Any idea?

Best regards,
Chao-Rui


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Unfortunately functionality like this requires end-to-end supports for this
change.  Not only do you need to be able to extend the backend device (lvextend,
like you did), you need Xen to see it (probably the feature you mentioned), you
need the guest kernel to see it, and you need the filesystem to be able to
expand.  Getting the guest kernel to see the change has always been the tricky
piece, as the kernel usually locks this information in and you have to reboot
for it to reread the information.  However, I saw some patches recently for the
Linux kernel that allow for on-the-fly resizing of disks, and I think I actually
tried it with some amount of success.  I wish I still had the links - I would
point you in the direction of them.

Other guest operating systems will vary on whether they support this or not. 
Windows is usually pretty good about detecting size changes for disks and
allowing you to expand the filesystem.  Other O/Ss will vary.

-Nick
>>> On 2010/04/12 at 21:39, Chao-Rui Chang <ppc52776@gmail.com>
wrote:
> Hello all,
> 
> I just notice the new feature in the latest version 4 release.
> 
> Any one know how to do this ?
> 
> I have tried lvextend the partition size in dom0,
> but domU doesn''t see the change.
> I also need to reboot to make domU reread the block size.
> 
> Any idea?
> 
> Best regards,
> Chao-Rui



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On Tuesday 13 April 2010 16:27:44 Nick Couchman wrote:
> Unfortunately functionality like this requires end-to-end supports for this
>  change.  Not only do you need to be able to extend the backend device
>  (lvextend, like you did), you need Xen to see it (probably the feature you
>  mentioned), you need the guest kernel to see it, and you need the
>  filesystem to be able to expand.  Getting the guest kernel to see the
>  change has always been the tricky piece, as the kernel usually locks this
>  information in and you have to reboot for it to reread the information. 
>  However, I saw some patches recently for the Linux kernel that allow for
>  on-the-fly resizing of disks, and I think I actually tried it with some
>  amount of success.  I wish I still had the links - I would point you in
>  the direction of them.
The patches for the Linux Kernel have been included in the latest Suse patch-
set.
One thing with these is, though, that the new size isn''t noticed by the
guest
untill you actually access the disk.
A "ls" on the mount is sufficient for this.
> Other guest operating systems will vary on whether they support this or
>  not.  Windows is usually pretty good about detecting size changes for
>  disks and allowing you to expand the filesystem.  Other O/Ss will vary.
I doubt MS Windows will notice this change as it requires Driver-support in 
the guest-OS for this to work.

--
Joost
> 
> >>> On 2010/04/12 at 21:39, Chao-Rui Chang
<ppc52776@gmail.com> wrote:
> >
> > Hello all,
> >
> > I just notice the new feature in the latest version 4 release.
> >
> > Any one know how to do this ?
> >
> > I have tried lvextend the partition size in dom0,
> > but domU doesn''t see the change.
> > I also need to reboot to make domU reread the block size.
> >
> > Any idea?
> >
> > Best regards,
> > Chao-Rui
> 
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On Tue, Apr 13, 2010 at 11:39:24AM +0800, Chao-Rui Chang
wrote:
>    Hello all,
> 
>    I just notice the new feature in the latest version 4 release.
> 
>    Any one know how to do this ?
> 
>    I have tried lvextend the partition size in dom0,
>    but domU doesn''t see the change.
>    I also need to reboot to make domU reread the block size.
> 
>    Any idea?
> 
See xen-devel archives for more information about this.
Novell developers recently submitted kernel patches that allow live-resizing
domU disks.

There was a patch for both dom0 and domU kernels.
Note: Novell''s method doesn''t require any changes to Xen or
the toolstack.

-- Pasi


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> 
>> Other guest operating systems will vary on whether they support this or
>>  not.  Windows is usually pretty good about detecting size changes for
>>  disks and allowing you to expand the filesystem.  Other O/Ss will
vary.
> 
> I doubt MS Windows will notice this change as it requires Driver-support in
> the guest-OS for this to work.
> 
Actually, Windows *does* notice the size change correctly, at least in my
experience.

-Nick



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