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Re: [Xen-users] Re: [Xen-devel] tap:qcow causes dom-U to hang in 3.0.3

To: Julian Chesterfield <jac90@xxxxxxxxx>
Subject: Re: [Xen-users] Re: [Xen-devel] tap:qcow causes dom-U to hang in 3.0.3
From: Roland Paterson-Jones <roland@xxxxxxxxxxxx>
Date: Fri, 10 Nov 2006 16:17:01 +0200
Cc: Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
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Julian Chesterfield wrote:

Roland,

Can you also verify whether there's an active tapdisk process running in Dom0 for each tap:{aio,qcow} vbd. We are aware of a bug with the qcow implementation that we hope to submit a fix for very soon. It's likely that you are seeing the same issue.

To answer your question, yes, it does appear that a tapdisk process is still running (this is after the dom-U has hung):

[root@dom0-0-50-45-5d-6a-bc ~]# ps -aef | grep tapdisk
root 4135 1 0 15:42 ? 00:00:01 tapdisk /dev/xen/tapctrlwrite1 /dev/xen/tapctrlread1

There is only one tap device, and the pid is the same as the single candidate while the dom-U was still reachable.

The hand seems to occur on the first (significant?) disk write inside the dom-U. For example:

-bash-3.00# dd if=/dev/zero of=./test-10MB bs=1k count=$((10*1024))

Has hung the dom-U, and I can no longer console or ssh into the dom-U.

Interestingly, on the dom-U, the qcow file has shrunk from its pervious peak of > 1TB, and is now appearing modestly as:

[root@dom0-0-50-45-5d-6a-bc ~]# ls -als /mnt/instance_image_store_0/
total 1564432
     4 drwxr-xr-x  2 root root       4096 Nov 10 15:42 .
     8 drwxr-xr-x  8 root root       4096 Nov  7 17:56 ..
1563132 -rw-r--r--  1 root root 1599078400 Nov 10 15:42 2
  1288 -rw-r--r--  1 root root    2466816 Nov 10 16:09 2.qcow

It's all very confusing. I'd love it to work, of course. Let me know what I can do to help with a diagnosis.

I'm running on the (binary) PAE-enabled 3.0.3 release.

Thanks and kind regards
Roland

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