Hi Simone,
Whenever you create a snapshot disk it will increase the length of the
"snapshot chain" by 1 and there is a hard length limit of 30. However whenever
you delete a snapshot disk the background "coalesce" process should be able to
reduce the "snapshot chain" length again. So your procedure (create snapshot;
export snapshot; delete snapshot) ought to work fine. This is in fact the same
process followed by the "VM protection and recovery" feature which will be part
of XCP 1.0.
The problem you linked to is related but not quite the same: it refers to a
limitation within the "coalesce" process where it cannot reduce a chain of
length 2 into a chain of length 1. The only reason people worry about this is
because a chain of length 2 can take up a lot more space on LVM where there is
no "thin provisioning" - this isn't a problem for you on NFS.
Given your observation that this only happens to VMs with more than 1 attached
virtual disk, I think you've found a bug in the tool which you used to add the
second disk to the VM. When you delete a VM snapshot (or uninstall a VM or
template generally), only those disks which have a special flag set are
actually deleted (specifically those with VBD.other-config:owner IIRC). If you
use the "xe vm-disk-add" CLI command it should set this flag. If this flag
isn't set then it would cause the additional disks not to be deleted... this
would cause your "snapshot chain" to get ever bigger, hit 30 and then fail.
I think a workaround is to identify the disk (VDI not VM) snapshots which
haven't been deleted and delete them manually, possibly via the CLI ("xe
vdi-destroy"). After a short while the background "coalesce" process should
kick in and reduce your chain lengths again.
Cheers,
Dave
From: [email protected]
[mailto:[email protected]] On Behalf Of Simone Cariani
Sent: 12 November 2010 12:00
To: [email protected]; [email protected]
Subject: [Xen-API] problem with snapshot unallocation
Hi all,
i use XCP 0.5 with a NFS storage repository and normally i do daily snapshots
from all VMs i have, as follow:
1) create snapshot
2) export snapshot to file
3) delete snapshot
One day I get the VM error "Snapshot chain is too long". I notice however that
this appears to only VM's with more than 1 attached virtual disk. In my case I
have a couple VM's with 2 disks, and there were many orphaned copies of only 1
of the 2 disks. >From OpenXenManager is not possible to delete these
snapshots..
I read a problem like this on Xencenter forum
http://forums.citrix.com/thread.jspa?threadID=261023&tstart=0
and the solution is
http://support.citrix.com/article/CTX123400
Does someone know how to fix this bug on XCP 0.5 ?
Regards,
Simone Cariani
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