[Openstack-operators] Overselling/Oversubscribing RAM

Joe Topjian joe.topjian at cybera.ca
Mon Sep 24 18:43:05 UTC 2012


Hi Diego,

Thank you for explaining this from StackOps' perspective.


Joe

On Mon, Sep 24, 2012 at 10:12 AM, Diego Parrilla Santamaría <
diego.parrilla.santamaria at gmail.com> wrote:

> Yes, overcommiting or not overcommiting RAM: that is the question ;-)
>
> The only reason for not recommending memory overcommitment is because it's
> hard to define a good Service Level Agreement.
>
> KVM does allow memory overcommitment and it works. We can guarantee it.
> KSM works (http://www.linux-kvm.org/page/KSM). But it's difficult to
> predict the performance impact of this technique. Hence, we can find
> situations where a Service Provider using StackOps Enterprise Edition
> (Openstack Nova on steroids  in the end) can complain of unexpected bad
> performance because a customer uses big Windows VMs in a physical server
> mixed with FreeBSD and Linux, for example.
>
> So, if you can live without strict SLAs, no problem. But if your business
> relies on SLAs signed with end customers, you should better avoid memory
> overcommitment. RAM is not so expensive and may be you can overcommit
> storage instead, for example.
>
> Cheers
> Diego
>
> P.D.: What I don't recommend in any way is overselling resources.
> Overcommitting must be a very controlled technique. I consider overselling
> an abuse.
>  --
> Diego Parrilla
>  <http://www.stackops.com/>*CEO*
> *www.stackops.com | * diego.parrilla at stackops.com** | +34 649 94 43 29 |
> skype:diegoparrilla*
> * <http://www.stackops.com/>
> *
>
> *
>
>
>
>
> On Mon, Sep 24, 2012 at 5:40 PM, Joe Topjian <joe.topjian at cybera.ca>wrote:
>
>> Hi Diego,
>>
>> Thank you for the link.
>>
>> Can you comment further on why you do not recommend overcommitting RAM?
>>
>> By default, OpenStack overcommits RAM by a ratio of 1.5. Do you change
>> this setting to 1?
>>
>> What kind of side effects have you seen from overcommitting?
>>
>> Thanks,
>> Joe
>>
>>
>> On Mon, Sep 24, 2012 at 1:57 AM, Diego Parrilla Santamaría <
>> diego.parrilla.santamaria at gmail.com> wrote:
>>
>>> Hi all,
>>>
>>> We wrote several months ago a quick overview about how to oversubscribe
>>> with StackOps Enterprise Edition. Surprisingly it was a presentation our
>>> customer they love :-o
>>>
>>> Here goes the presentation in slideshare:
>>>
>>> http://www.slideshare.net/stackops/stackops-openstack-nova-sizing-service-definition
>>>
>>> Cheers
>>> Diego
>>>  --
>>> Diego Parrilla
>>>  <http://www.stackops.com/>*CEO*
>>> *www.stackops.com | * diego.parrilla at stackops.com** | +34 649 94 43 29|
>>> skype:diegoparrilla*
>>> * <http://www.stackops.com/>
>>> *
>>>
>>> *
>>>
>>>
>>>
>>>
>>> On Fri, Sep 21, 2012 at 4:39 PM, Samuel Winchenbach <swinchen at gmail.com>wrote:
>>>
>>>> Hi All,
>>>>
>>>> What are some "best practices" when it comes to overselling RAM in a
>>>> KVM based openstack setup?  For example:
>>>>
>>>> I have 4 nodes with 16 cores & 128 GB RAM each.  If on one of those
>>>> nodes I oversell ram 2:1 (256 GB RAM) and the VMs actually use that
>>>> much does it just start swapping out pages to disk?
>>>>
>>>> How do all of you handle overselling RAM?
>>>>
>>>> Thanks,
>>>> Sam
>>>>
>>>> _______________________________________________
>>>> OpenStack-operators mailing list
>>>> OpenStack-operators at lists.openstack.org
>>>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators
>>>>
>>>
>>>
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>>>
>>>
>>
>>
>> --
>> Joe Topjian
>> Systems Administrator
>> Cybera Inc.
>>
>> www.cybera.ca
>>
>> Big data is coming to Canada. Join the welcome wagon.
>> *Cyber Summit 2012*
>> October 1-3, Banff
>> www.cybera.ca/summit2012
>>
>> Cybera is a not-for-profit organization that works to spur and support
>> innovation, for the economic benefit of Alberta, through the use
>> of cyberinfrastructure.
>>
>>
>> _______________________________________________
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>>
>>
>


-- 
Joe Topjian
Systems Administrator
Cybera Inc.

www.cybera.ca

Big data is coming to Canada. Join the welcome wagon.
*Cyber Summit 2012*
October 1-3, Banff
www.cybera.ca/summit2012

Cybera is a not-for-profit organization that works to spur and support
innovation, for the economic benefit of Alberta, through the use
of cyberinfrastructure.
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