I was using Xen guest tools, but not for a System VM.  Instead, I was using the 
VM to write disk images to volumes from within my CloudStack account. 

Details of the bug are below.  

Changing from Debian 7.0 to Debian6.0.5 appears to have solved problem.


...


Donal Lafferty  -  6/18/12 6:42:10 PM

os.fsync is not properly supported by the underlying Dom0 drivers.  Problem 
seems to be that they do not advertise the feature-flush-cache capability.  
Instead, they advertise feature-barriers, but they do not implement it.  As a 
result, you get the following messages:

Jun 18 23:53:39 debian70min kernel: [  186.884574] blkfront: barrier: empty 
write xvdc op failed
Jun 18 23:53:39 debian70min kernel: [  186.884587] blkfront: xvdc: barrier or 
flush: disabled
Jun 18 23:53:39 debian70min kernel: [  187.355316] vbd vbd-51744: 16 Device in 
use; refusing to close
Jun 18 23:53:39 debian70min kernel: [  187.414507] block xvdc: releasing disk

See https://bugs.launchpad.net/ubuntu/+source/linux/+bug/824089 a good 
description of the issue is in comment #41.

Other references:  http://www.gossamer-threads.com/lists/xen/users/226266 found 
via 
http://xen.1045712.n5.nabble.com/Xen-block-drivers-and-barrier-support-td5709209.html

Donal Lafferty  -  6/22/12 9:10:55 AM

Updated workerVM O/S to Debian6.0.5.  The messages in /var/log now say:

Jun 22 13:53:35 workerVM kernel: [   51.765136] blkfront: xvdc: barriers enabled

Tested that Attach / Detach errors no longer occur.



> -----Original Message-----
> From: Musayev, Ilya [mailto:[email protected]]
> Sent: 18 January 2013 16:47
> To: [email protected]
> Subject: RE: Build SystemVM template
> 
> Donal,
> 
> Did you have Xen guest tool installed on system VM?
> 
> Thanks
> ilya
> 
> -----Original Message-----
> From: Donal Lafferty [mailto:[email protected]]
> Sent: Friday, January 18, 2013 6:15 AM
> To: [email protected]
> Subject: RE: Build SystemVM template
> 
> You might want to check the XenServer support.
> 
> I had problems with detaching VDIs on Wheezy on XenServer March/April
> 2012.  There was no reason to report the problem at the time, because
> XenServer didn't cite Wheezy as a supported guest OS.  Also, I expect I was
> using an older build.
> 
> DL
> 
> > -----Original Message-----
> > From: Rohit Yadav [mailto:[email protected]]
> > Sent: 18 January 2013 02:47
> > To: [email protected]
> > Subject: Re: Build SystemVM template
> >
> >
> > On 17-Jan-2013, at 6:10 PM, Sheng Yang <[email protected]> wrote:
> >
> > > On Thu, Jan 17, 2013 at 5:07 PM, Rohit Yadav
> > > <[email protected]>
> > wrote:
> > >> Hi Sheng, we can reuse viewee and vagrant based appliance building
> > >> code
> > for devcloud for systemvm. We can use debian wheezy i386 beta4 for now
> > and when it releases in february we can have another round of
> > building/testing.
> > >
> > > Sure, is there a document for it? Also, I didn't see a release date
> > > for Wheezy... Do you have reference?
> >
> > tools/devcloud/README.md (it can have bugs, help fix it wherever you
> > see
> > improvement) Once you build systemvm, you can export and convert the
> > disk image from vmdk/vhd to qcow2/vhd/vmdk etc.
> > Wheezy should release in Feb like the last two releases in 2009 and
> > 2011, but it's not confirmed.
> >
> > Regards.
> >
> > >
> > > --Sheng
> > >>
> > >> Regards.
> > >>
> > >> On 17-Jan-2013, at 4:18 PM, Sheng Yang <[email protected]> wrote:
> > >>
> > >>> Hi,
> > >>>
> > >>> I just found the buildsystemvm.sh won't work, and I need to build
> > >>> a new systemvm template for IPv6 support, because we're adding
> new
> > >>> softwares in it.
> > >>>
> > >>> Apparently due to license issue(I guess),xt_CHECKSUM.ko which is a
> > >>> extension of iptables to fix one Debian/Ubuntu DHCP issue. I
> > >>> believe the iptables_1.4.8-3local1checksum1_i386.deb(a patched
> > >>> version of iptables by us) is also removed, as well as
> > >>> xe-guest-utilities_5.6.0-595_i386.deb.
> > >>>
> > >>> So, what we suppose to do to make systemvm template buildable
> again?
> > >>> I know there are some licenses issues involved, but not quite
> > >>> clear on these.
> > >>>
> > >>> --Sheng
> > >>
> 
> 

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