Xen users - May 2008 - Live migration not moving the disk image. Is is supposed to?

>From my reading, it looks like performing "xm migrate -live domU
target_server" ought to also copy the disk image.  Am I right? 

 

When I attempt this procedure, everything looks to work except for the image
file getting moved.  The command takes about 30 seconds to complete and then
"xm list" shows the domU to be gone from the old host and running on
the new
host.  The SSH connection to the domU also continues to function without a
hiccup. However, the disk image isn''t located anywhere on the new
server.
Also, the xen log on the new server lists the following error:

 

[2008-05-15 19:10:21 xend 3790] ERROR (XendCheckpoint:275) Device 51712
(tap) could not be connected.

/virt/myserver.img does not exist

Traceback (most recent call last):

  File
"/usr/lib64/python2.4/site-packages/xen/xend/XendCheckpoint.py", line
273, in restore

    dominfo.waitForDevices() # Wait for backends to set up

  File
"/usr/lib64/python2.4/site-packages/xen/xend/XendDomainInfo.py", line
1760, in waitForDevices

    self.waitForDevices_(c)

  File
"/usr/lib64/python2.4/site-packages/xen/xend/XendDomainInfo.py", line
1158, in waitForDevices_

    return self.getDeviceController(deviceClass).waitForDevices()

  File
"/usr/lib64/python2.4/site-packages/xen/xend/server/DevController.py",
line
145, in waitForDevices

    return map(self.waitForDevice, self.deviceIDs())

  File
"/usr/lib64/python2.4/site-packages/xen/xend/server/DevController.py",
line
179, in waitForDevice

    raise VmError("Device %s (%s) could not be connected.\n%s" %

VmError: Device 51712 (tap) could not be connected.

/virt/myserver.img does not exist

 

I then attempt to execute on the domU that accesses the disk ("df",
for
example) and the instance hangs.

 

Both servers are running the 64-bit version of CentOS and using the xen
packages from the yum repos.  On the source server, "/virt" is mounted
on an
ext3 filesystem in an LVM volume.  "/virt" on the target server is
also
ext3, but without LVM.  Would this have any affect? The domU config file is
pretty basic:

 

name = "myserver"

uuid = "42db455d-17be-5288-cf89-7820ddcd0c76"

maxmem = 512

memory = 512

vcpus = 1

bootloader = "/usr/bin/pygrub"

on_poweroff = "destroy"

on_reboot = "restart"

on_crash = "restart"

vfb = [ "type=vnc,vncunused=1" ]

disk = [ "tap:aio:/virt/myserver.img,xvda,w" ]

vif = [ "mac=00:16:3e:1e:94:fb,bridge=xenbr0" ]

 



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On Thu, 15 May 2008, Jamie J. Begin wrote:
> >From my reading, it looks like performing "xm migrate -live domU
> target_server" ought to also copy the disk image.  Am I right?
>
> When I attempt this procedure, everything looks to work except for the
image
> file getting moved.  The command takes about 30 seconds to complete and
then
> "xm list" shows the domU to be gone from the old host and running
on the new
> host.  The SSH connection to the domU also continues to function without a
> hiccup. However, the disk image isn''t located anywhere on the new
server.
> Also, the xen log on the new server lists the following error:
>
> [2008-05-15 19:10:21 xend 3790] ERROR (XendCheckpoint:275) Device 51712
> (tap) could not be connected.
>
> /virt/myserver.img does not exist
That sounds pretty much like expected behavior. This is why you require
something like NFS, DRBD, iSCSI to have the storage available over more
than one machine at a time.


Stefan


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> -----Original Message-----
> From: Stefan de Konink [mailto:skinkie@xs4all.nl]
> Sent: Thursday, May 15, 2008 7:28 PM
> To: Jamie J. Begin
> Cc: xen-users@lists.xensource.com
> Subject: Re: [Xen-users] Live migration not moving the disk image. Is is
> supposed to?
> 
> On Thu, 15 May 2008, Jamie J. Begin wrote:
> 
> > >From my reading, it looks like performing "xm migrate -live
domU
> > target_server" ought to also copy the disk image.  Am I right?
> >
> > When I attempt this procedure, everything looks to work except for the
> image
> > file getting moved.  The command takes about 30 seconds to complete
and
> then
> > "xm list" shows the domU to be gone from the old host and
running on the
> new
> > host.  The SSH connection to the domU also continues to function
without
> a
> > hiccup. However, the disk image isn''t located anywhere on the
new
> server.
> > Also, the xen log on the new server lists the following error:
> >
> > [2008-05-15 19:10:21 xend 3790] ERROR (XendCheckpoint:275) Device
51712
> > (tap) could not be connected.
> >
> > /virt/myserver.img does not exist
> 
> That sounds pretty much like expected behavior. This is why you require
> something like NFS, DRBD, iSCSI to have the storage available over more
> than one machine at a time.
> 
> 
> Stefan
Ok, thanks. I just wanted to make sure that this was expected behavior.
Yeah, iSCSI is forthcoming for the production environment.  I''m just
testing
a few things here.


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> > From: Stefan de Konink [mailto:skinkie@xs4all.nl]
> > Sent: Thursday, May 15, 2008 7:28 PM
> > To: Jamie J. Begin
> > Cc: xen-users@lists.xensource.com
> > Subject: Re: [Xen-users] Live migration not moving the disk image. Is
is
> > supposed to?
> >
> > On Thu, 15 May 2008, Jamie J. Begin wrote:
> > > >From my reading, it looks like performing "xm migrate
-live domU
> > >
> > > target_server" ought to also copy the disk image.  Am I
right?
> > >
> > > When I attempt this procedure, everything looks to work except
for the
> >
> > image
> >
> > > file getting moved.  The command takes about 30 seconds to
complete and
> >
> > then
> >
> > > "xm list" shows the domU to be gone from the old host
and running on
> > > the
> >
> > new
> >
> > > host.  The SSH connection to the domU also continues to function
> > > without
> >
> > a
> >
> > > hiccup. However, the disk image isn''t located anywhere
on the new
> >
> > server.
> >
> > > Also, the xen log on the new server lists the following error:
> > >
> > > [2008-05-15 19:10:21 xend 3790] ERROR (XendCheckpoint:275) Device
51712
> > > (tap) could not be connected.
> > >
> > > /virt/myserver.img does not exist
> >
> > That sounds pretty much like expected behavior. This is why you
require
> > something like NFS, DRBD, iSCSI to have the storage available over
more
> > than one machine at a time.
> >
> >
> > Stefan
>
> Ok, thanks. I just wanted to make sure that this was expected behavior.
> Yeah, iSCSI is forthcoming for the production environment.  I''m
just
> testing a few things here.
You do need to have the storage accessible from multiple machines in order to 
support live migration.  You can either do this by having dom0 access the 
storage (e.g. over SAN or network) and export it to the domU as a VBD (I 
recommend this, it''s more transparent) or by setting up the domU to
access
its storage directly over the network (e.g. using iSCSI root or NFS root).

Xen includes some NBD-aware block scripts to make it easy to handle NBD-based 
block devices in an automated way.  Stefan has, I believe, published some 
iSCSI (and Netapp filer specific) block scripts on these mailing lists, which 
may also prove useful.

Cheers,
Mark

-- 
Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)

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