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Re: [libvirt] [PATCH 0/6] Support online block resizing



On Thu, Sep 01, 2011 at 02:14:23PM +0100, Daniel P. Berrange wrote:
> On Wed, Aug 31, 2011 at 09:31:58PM +0800, Osier Yang wrote:
> > Upstream QEMU introduced online block resizing to resize the
> > block device when domain is running since commit 6d4a2b3a4795.
> > It simply reuses existing "bdrv_truncate" method which is used
> > by "qemu-img" to resize the images. This means it supports to
> > resize all the format that "qemu-img resize" supports. E.g.
> > qcow2, raw, qed, qcow, etc. (NB, it doesn't support to shrink
> > size of qcow2 image, and QEMU reports "An undefined error
> > has ocurred" in this case).
> > 
> > For block device of virtio bus, the guest can update the device
> > size automatically, needs kernel support, since kernel-2.6.32-117:
> > 
> >   http://patchwork.usersys.redhat.com/patch/33040/
> > 
> > For block device of SCSI bus, one needs to execute command like
> > below in the guest (linux) to update the size:
> > 
> >   % echo > /sys/class/scsi_device/0:0:0:0/device/rescan
> > 
> > For block device of IDE bus, seems there is no way to let guest
> > update the size after resizing.
> 
> Your API proprosal looks reasonable, but unfortunately the QEMU
> command 'block_resize' is either broken, or incomplete since it
> does not have a way to notify the guest that a block device has
> been resized, independantly of actually resizing the host file.
> This is required in order for guest disk resize to work on LVM,
> SCSI, iSCSI, etc block devices, since QEMU cannot itself do a
> resize of the block devices. The resize has to be done either
> by libvirt using host commands, or by the SAN administrator on
> the remote storage appliance.
> 
> IMHO, we should not commit to the libvirt API design, until we
> can get confirmation from QEMU about whether they will fix the
> block_resize command to work for block devices, or add a new
> command for just notifying guests of external block device
> resizes

See this thread...

http://lists.nongnu.org/archive/html/qemu-devel/2011-09/msg00068.html


Daniel
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