[Qemu-devel] Re: Block device resize detection

[Vandeir Eduardo]

Humm,

unfortunately I'm not a developer, only a sys admin, but this would
be a nice feature to avoid restarting vm guests.

I didn't want, but I think I will have to add another
software layer (LVM) inside the guest vm.
This way, when I need more space, I hot-add another device and
add it to the volume group of the guest vm.

Thanks.

On Mon, 6 Dec 2010, Alexander Graf wrote:

> Hi Vandeir,
> 
> 
> On 06.12.2010, at 11:49, Vandeir Eduardo wrote:
> 
> > Hi guys,
> > 
> > I have a KVM guest machine, lets name it VMTEST,
> > using an iSCSI LUN as a virtio device. Something like this:
> > 
> > <disk type='block' device='disk'>
> >   <driver name='qemu' type='raw' cache='none'/>
> >   <source 
> > dev='/dev/disk/by-path/ip-w.x.y.z:3260-iscsi-iqn.2010-10.br.furb.inf:disk0-lun-4'/>
> >      <target dev='vda' bus='virtio'/>
> > </disk>
> > 
> > On iSCSI server, if I resize this LUN, this resize is detected
> > on KVM host, but not on the VMTEST. The device resize is only
> > detected if I restart VMTEST. Is there a way to make VMTEST detect
> > the /dev/vda resize without restarting it?
> > 
> > On VMTEST I already tried commands like partprobe /dev/vda, 
> > hdparm -z /dev/vda and blockdev --rereadpt /dev/vda, but none of
> > was capable to detect the block device (/dev/vda) resize.
> 
> The probing of an image is only done at initialization time of the block 
> backend driver, which in your case is the bootup. The only chance you have of 
> reevaluating it would be to hot-add another virtio device with the resized 
> image.
> 
> Alternatively, you could also try to write a patch for reevaluation plumbing, 
> so that the hba emulation layer can trigger reevaluation in the disk layer.
> 
> 
> Alex
> 
> 

__________________________________________
Vandeir Eduardo
(CCNA, LPIC-2, MCSA 2003 Server)
Laboratório de Computação e Informática (LCI) - Campus III
Fundacao Universidade Regional de Blumenau (FURB)
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