Snapshots with 'disk and memory' take a very long time? / calcru: runtime went backwards

Karl Pielorz kpielorz_lst at
Thu Aug 29 10:13:29 UTC 2013

Now we've got the ability to take snapshots with 'memory' - they seem to 
take a very long time...

Setup is FreeBSD 9.2-RC3 amd64 XENHVM system running under Xen Server 6.2, 
on a reasonably fast machine (all SSD storage).

In XenCenter a 'disk snapshot' completes in 3 seconds, however selecting 
'Snapshot the virtual machine's disks and memory' takes over a minute?

We're new to Xen - so I've no idea if that's a good, or bad time? - The 
guest host goes comatose while it's happening as well.

Also once the snapshot is complete the console starts filling with lots of:

calcru: runtime went backwards from 752 usec to 717 usec for pid X

(Lots of values for 'from' and 'to' and lots, i.e. all PID's).

Restarting the VM fixes this.

Any pointers? - aside from switching the kernel to XENHVM, installing 
'xe-guest-utilities' and 'removing' the CDROM drive from the image - it's 
all stock settings.



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