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From Dag Sonstebo <>
Subject Re: Amount of virtual machines per host
Date Thu, 05 Jul 2018 09:04:30 GMT
Hi Dmitri,

This depends on so many factors that only you yourself can answer this. Your VM density all
depends on the spec of your hardware, your overprovisioning of RAM/CPU and also very much
on what size and workloads your VMs run and how much disk activity they have. When you on
top of this make CloudStack management compete for resources with KVM on the same box then
sooner or later one of your resources will start to run low – in your case it’s impossible
to say without looking at the performance stats on your server – it could be CPU, RAM or
disk I/O. A density of 450 VMs / server is not something we see often – I guess theoretically
this could be achieved on light workloads and high spec servers – but most CloudStack users
will run with lower figures than this.

Transactions from secondary storage to primary storage: in short the first time a template
is used it is copied by the hypervisor from secondary (where it was uploaded to) to primary.
The second time it is used CloudStack checks if the template is already in the chosen primary
pool and if it is just uses the existing copy for linked clone. The Secondary Storage VM is
mainly there to handle uploads and downloads to secondary storage as well as some snapshot

Hope this helps,

Dag Sonstebo
Cloud Architect

On 05/07/2018, 08:46, "Dmitry Berezhnoy" <> wrote:

    I have installed cloudstack-management, cloudstack-agent(KVM hypervisor)
    and nfs-server at the same physical server. Then I have created virtual
    machines one by one in 8 parallel threads. For each thread I created shared
    network(VR). This server has two SSDs with ZFS filesystem. Copying files
    and disk speed is good enough (not only in system idle), but when I have
    450 virtual machines the next one has been creating during 5 minutes, is it
    correct work? This time becomes too long on 200 (about a minute) virtual
    machines and increase on every 10 machines or so. Does anybody have any
    ideas how to make it faster?
    Here is another question: how transaction from secondary storage to primary
    works. I see that images on primary are something like delta from original
    image (deduplicated?). Which component of Cloudstack is responsible for
    transfering data from secondary to primary?
    Thanks in advance for any ideas and info.
    Best regards,
53 Chandos Place, Covent Garden, London  WC2N 4HSUK

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