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From Yong Chen <>
Subject The snapshot chain is too long
Date Mon, 15 Jul 2013 00:43:50 GMT

I'm using CS 4.0.1 and XS 6.0.2. There is a problem with taking snapshots of instances.

Some of VMs have scheduled snapshots (e.g. weekly, monthly) so  eventually there will be quite
some number of snapshots on secondary storage. This is fine as I read CloudStack should copy
snapshots to secondary storage and then coalesce snapshots on primary storage so can keep
the chain not too long (like 3-4 child normally).

However I found after snapshot been taken for a while it starts failing due to error logged
on CS Management log 'SR_BACKEND_FAILURE_109The snapshot chain is too long'. I verified it
by checking with vhd-util and it does show the affected VHD has exactly 30 snapshots in chain
which is the limit for XenServer.

I tried to search for info why the chain can grow to 30 and only found this article for CloudStack
2.2 seems to be related. It mentioned there maybe
problem preventing XenServer from cleaning up snapshots. However I can't find any more error
info other than CS Management log 'SR_BACKEND_FAILURE_109The snapshot chain is too long'.

What can cause XenServer or CloudStack not cleaning up snapshots from primary storage? Thanks
in advance.


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