Xen users - Jul 2008 - Handling virtual disks on Xen

Hello everyone,

Im starting to use Xen on a SUSE Linux Enterprise Server 10 SP2, but Im not
quite happy yet with the virtual disk management. I still need to do a lot
of research about that, but first I want to ask the community about a simple
way to handle the guest machine disks.

*Is there any way to increase/decrease a guest machine disk after the OS is
installed? Can I have a dynamically expanding disk when I create a virtual
machine?*

Any best practices that you can give me regarding to that?

Thanks in advance!


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On 07/07/2008 21:18, Augusto Alvarez wrote:
> *Is there any way to increase/decrease a guest machine disk after the OS 
> is installed? Can I have a dynamically expanding disk when I create a 
> virtual machine?*
if you use LVM, you can create an LV for each "disk" you want a domU
to
have, you can then expand the LV and then expand the filesystem iside it 
(or reduce the filesystem, then reduce the LV)

Unfortunately the last time I checked xen doesn''t report the changed LV
size "live" to the domU, so you''ll need a reboot of the domU.


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> On 07/07/2008 21:18, Augusto Alvarez wrote:
> 
> > *Is there any way to increase/decrease a guest machine disk after
the OS
> > is installed? Can I have a dynamically expanding disk when I create
a
> > virtual machine?*
> 
> if you use LVM, you can create an LV for each "disk" you want a
domU
to
> have, you can then expand the LV and then expand the filesystem iside
it
> (or reduce the filesystem, then reduce the LV)
> 
> Unfortunately the last time I checked xen doesn''t report the
changed
LV
> size "live" to the domU, so you''ll need a reboot of the
domU.
> 
Even if it did, can Linux handle it anyway? I added a disk to a RAID
array recently and while I could use fdisk to add a new partition, I had
to reboot before Linux could use it.

James

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On Monday 07 July 2008, James Harper wrote:
> Even if it did, can Linux handle it anyway? I added a disk to a RAID
> array recently and while I could use fdisk to add a new partition, I had
> to reboot before Linux could use it.
partprobe

-- 
Javier


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> On Monday 07 July 2008, James Harper wrote:
> > Even if it did, can Linux handle it anyway? I added a disk to a RAID
> > array recently and while I could use fdisk to add a new partition, I
had
> > to reboot before Linux could use it.
> 
> partprobe
> 
Please correct me if I''m wrong, but doesn''t partprobe just ask
Linux to
re-read the partition table? This is exactly what fdisk does, but it
fails if the disk is already in use, which is the case we are discussing
here.

James

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On Mon, Jul 7, 2008 at 6:38 PM, James Harper
<james.harper@bendigoit.com.au>
wrote:
> > On Monday 07 July 2008, James Harper wrote:
> > > Even if it did, can Linux handle it anyway? I added a disk to a
RAID
> > > array recently and while I could use fdisk to add a new
partition, I
> had
> > > to reboot before Linux could use it.
> >
> > partprobe
> >
>
> Please correct me if I''m wrong, but doesn''t partprobe
just ask Linux to
> re-read the partition table? This is exactly what fdisk does, but it
> fails if the disk is already in use, which is the case we are discussing
> here.
>
> James
>
> _
>
I''m not entirely sure what partprobe does but I know you can get rid of
99%
of the times that you would have to reboot after editing the partition
table by using it. Very rarely will partprobe not update the partition table
list in the kernel. It''s been a godsend. On the other hand you can go
back in and edit a disk with fdisk after already previously editing it but
you won''t be able to format the partitions without using partprobe or
rebooting.

Grant


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On 08/07/2008 02:07, James Harper wrote:
> Even if it did, can Linux handle it anyway?
Windows certainly can, On VMware (would work on bare metal too) I have 
disks connected via the iSCSI initiator, can increase the size of the 
target, refresh within Disk Management or diskpart.exe and extend the 
volume without a reboot - provided it''s not a system disk.

I haven''t tried it on Xen with an LVM/phy: disk to a Windows domU
(yet).



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Javier Guerra Giraldez schrieb:
> On Monday 07 July 2008, James Harper wrote:
>> Even if it did, can Linux handle it anyway? I added a disk to a RAID
>> array recently and while I could use fdisk to add a new partition, I
had
>> to reboot before Linux could use it.
> 
> partprobe
This requires parted package to be installed. On bare system the same
effect can be achieved by calling blockdev --rereadpt /dev/mydevice.
blockdev is part of util-linux.

The said methods do not work while the disk pt is open. Resizing LVM
however doesn''t have the need for rebooting the dom0 as the changes are
applied dynamically in the dom0. The domU however has still to be
booted, AFAIK. There is xm block-reconfigure which might update the disk
size, but that didn''t work for me as of Xen 3.2.0.

MfG
-Dimitri Puzin
> 
> 
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