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From Andrei Mikhailovsky <and...@arhont.com.INVALID>
Subject Re: KVM Live VM Snapshots
Date Tue, 27 Dec 2016 22:18:00 GMT
Hi Marco,

While i totally agree with you on the design and resiliance to failures of newly developed
apps, I disagree with you on the necessity to have a vm snapshot feature with kvm. and let
me explain why.

At the moment, I am running a small acs + kvm + ceph cluster with about a hundred or so vms.
Currently, it is a huge problem for me to perform vm snapshots in a reasonably good state,
especially if vm has multiple volumes. The problem with ACS implementation (which is not present
in openstack for example) is that there is no way I can keep the snapshots on the primary
storage (using fast interconnect). The snapshots are copied over a slow link to the nfs secondary
storage. It takes ages to perform any operation with the secondary storage due to its silly
design (even though I see the reason for its existence in some cases). Now, consider that
I have to take a daily snapshot of every volume and some volumes have to snapped on an hourly
basis. This totally overloads the network + nfs storage. Imagine that you have to recover
a few volumes from snapshots or create new volumes or templates from them while the daily/hourly
snapshot cycle is taking place. You will have to wait hours before you get anywhere even on
smaller size volumes.

However, when I was testing the XenServer setup with the VM snapshot capability, the snapshot
creation and roll back was pretty quick. and it worked for all disk volumes in that vm. I
don't remember seeing much network traffic or load on the nfs server either. This feature
is a must imho regardless of the application design. Besides, as far as I remember, the KVM
have that capability, so, why not implement it within ACS, just like it's done for vmware
and xenserver?

Andrei

----- Original Message -----
> From: "Marc-Aurèle Brothier" <marco@exoscale.ch>
> To: "users" <users@cloudstack.apache.org>
> Sent: Monday, 19 December, 2016 08:31:26
> Subject: Re: KVM Live VM Snapshots

> Hi Asai,
> 
> In my opinion, doing a VM snapshot is making a step in the wrong direction.
> Your applications/system running inside your VMs should be designed to
> handle an OS crash. Then a new VM, freshly installed, should be able to get
> back into your application setup so that you have again an appropriate
> number of healthy nodes.
> 
> Marco
> 
> On Mon, Dec 19, 2016 at 4:34 AM, Asai <asai@globalchangemusic.org> wrote:
> 
>> Greetings,
>>
>> Is it correct that currently there is no support in Cloudstack for KVM
>> live VM snapshots? I see that Volume snapshots are available for running
>> VMs, but that makes me wonder what everyone is doing to get a disaster
>> recovery backup of a KVM based VM?  I did ask this question a few weeks
>> back, but only one person responded with one solution, and I am really
>> trying to figure out what the best solutions are here.
>>
>> Has anybody seen this script? https://gist.github.com/ringe/
>> 334ee88ba5451c8f5732
>>
>> What is the community's opinion of scripts like this?  And also, big
>> question, if this script is good, why isn't it integrated into Cloudstack?
>>
>> Thanks,
>> Asai
>>

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