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From Timothy Lothering <>
Subject RE: Deployment failed on XenServer due to capacity miscalculation
Date Fri, 10 Jul 2015 11:11:43 GMT
Thanks Martin,

Could you please dump your full logs somewhere so we can look into this further?

-----Original Message-----
From: Martin Emrich [] 
Sent: 09 July 2015 03:49 PM
Subject: Re: Deployment failed on XenServer due to capacity miscalculation


Am 08.07.2015 um 16:15 schrieb Timothy Lothering:
> Hi Martin,
> Thanks for the information.
>  From the details below, I understand that your Cluster will not allow additional VMs
to be created if 85% of the memory is consumed. This value is important as you also need to
factor in what amount of memory is required by the Hypervisor (XenServer) to run. Xenserver
needs a minimum of 1GB -- Check out the following link:

Correct. On the other host, only 60% is used, so still enough free space in the cluster. The
cluster actually allows new VMs, but tries to start them on the wrong host.

> Secondly, unless you are running memory intensive applications, using a 1:1 ratio is
not entirely economically viable, you can safely up the mem.overprovisioning.factor to 2 or
4 (depending on your Memory over provisioning calculations vs CPU). This means that you are
essentially doubling or quadrupling up on the actual amount of memory you have available.

We prefer to give our users the full memory they request. XenServer does no "real" memory
overprovisioning, but proportionally scales VMs down if the hosts real memory is exceeded.
Unless there's real dynamic memory scaling (including swapping, deduplication and pressure
sensing), we prefer to stay at 1:1.

> Another option to look at is your deployment.planners.order & vm.deployment.planner
fields. In my case, I use FirstFitPlanner for both as we prefer to fully utilize each host
before provisioning on another host.

That's what I prefer, too.

The problem is not that the algorithm is wrong, but that the data it bases its decisions on
is faulty. So not CloudStack fails to create VM, but the underlying XenServer.


Timothy Lothering
Solutions Architect
Managed Services

T: +27877415535
F: +27877415100
C: +27824904099


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