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From Remi Bergsma <>
Subject Remember this one? CLOUDSTACK-7319
Date Wed, 18 Feb 2015 15:46:17 GMT

This summer we had some serious issues with creating snapshots on XenServer, see CLOUDSTACK-7319
for details. Long story short, to copy the ‘dd’ command was used and that hammered dom0
until it would crash/fence. The script that did the copy at the time was vmopsSnapshot. We
added two flags: iflag=direct and oflag=direct. Problem solved from 4.4.0 and on you’d expect.

We just had a hypervisor crashing due to heavy dd load again. Eventually, it could not reach
the storage any more so it fenced.  When investigating, we found that the copy is now done
again without the direct flags. The reason is that the script has been removed and that a
xapi plugin is now used instead. Problem is that this does not use the direct flags :-s So
our issue is back.

def dd_vdi__(src_dev, dest_dev):
    os.system('dd if=/dev/%s of=/dev/%s bs=2M' % (src_dev, dest_dev))

We will be hot fixing all hypervisors and add the flags asap.

This happens from 4.4 and on if you’re using XenServer 6.2.5 (which is 6.2.0 with patch
XS62ESP1004). If you run this XenServer version, I’d patch the copy script asap.


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