Yes, overcommiting or not overcommiting RAM: that is the question ;-)<div><br></div><div>The only reason for not recommending memory overcommitment is because it's hard to define a good Service Level Agreement.</div><div>
<br></div><div>KVM does allow memory overcommitment and it works. We can guarantee it. KSM works (<a href="http://www.linux-kvm.org/page/KSM">http://www.linux-kvm.org/page/KSM</a>). 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. </div>
<div><br></div><div>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.</div>
<div><br></div><div>Cheers</div><div>Diego</div><div><br></div><div>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.</div>
<div> -- <br><span style="border-collapse:separate;font-family:Times"><span style="border-collapse:collapse;font-family:arial,sans-serif"><div align="left" style="font-size:13px"><div><font><span lang="ES" style="font-family:Arial">Diego Parrilla<br>
<a href="http://www.stackops.com/" title="file:///C:/Documents%20and%20Settings/carolina.capsir.per1/Application%20Data/Microsoft/Signatures/www.garrigues.com
www.garrigues.com" style="color:rgb(7,77,143)" target="_blank"><span title="file:///C:/Documents%20and%20Settings/carolina.capsir.per1/Application%20Data/Microsoft/Signatures/www.garrigues.com"></span></a></span></font><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><b>CEO</b><font size="1"><br>
</font></font><span style="border-collapse:separate;font-family:Times;font-size:medium"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"></span></span><b><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><a href="http://www.stackops.com/" target="_blank"><b>www.stackops.com</b></a> | </font></b><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><font size="1"> <a href="mailto:diego.parrilla@stackops.com" target="_blank">diego.parrilla@stackops.com</a></font></font><span style="border-collapse:separate;font-family:Times;font-size:medium"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"><font color="#004438" face="Arial"><b><b><span lang="EN-GB" style="font-size:10pt"></span></b></b></font></span></span><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><font size="1"> | </font></font><span style="border-collapse:separate;font-family:Times;font-size:medium"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><font size="1">+34 649 94 43 29 | <a>skype:diegoparrilla</a></font></font></span></span><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><a href="http://www.stackops.com/" target="_blank"><b><br>
</b></a></font></div></div><div style="font-size:13px"><font color="#004438" face="Arial"><b><p><span style="border-collapse:separate;color:rgb(0,0,0);font-family:Times;font-size:medium"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"><span style="border-collapse:separate;font-family:Times;font-size:medium"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"><font color="#004438" face="Arial"><b><b><span lang="EN-GB" style="font-size:10pt"><img src="http://stackops.s3-external-3.amazonaws.com/STACKOPSLOGO-ICON.png"></span></b></b></font></span></span></span></span></p>
</b></font></div></span></span><div><br></div><br>
<br><br><div class="gmail_quote">On Mon, Sep 24, 2012 at 5:40 PM, Joe Topjian <span dir="ltr"><<a href="mailto:joe.topjian@cybera.ca" target="_blank">joe.topjian@cybera.ca</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi Diego,<div><br></div><div>Thank you for the link.</div><div><br></div><div>Can you comment further on why you do not recommend overcommitting RAM? </div><div><br></div><div>By default, OpenStack overcommits RAM by a ratio of 1.5. Do you change this setting to 1?</div>
<div><br></div><div>What kind of side effects have you seen from overcommitting?</div><div><br></div><div>Thanks,</div><div>Joe</div><div><div><div class="h5"><br><br><div class="gmail_quote">On Mon, Sep 24, 2012 at 1:57 AM, Diego Parrilla Santamaría <span dir="ltr"><<a href="mailto:diego.parrilla.santamaria@gmail.com" target="_blank">diego.parrilla.santamaria@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi all,<div><br></div><div>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</div>
<div><br></div><div>Here goes the presentation in slideshare:</div>
<div><a href="http://www.slideshare.net/stackops/stackops-openstack-nova-sizing-service-definition" target="_blank">http://www.slideshare.net/stackops/stackops-openstack-nova-sizing-service-definition</a></div><div><br></div>
<div>Cheers</div>
<div>Diego<br clear="all"> -- <br><span style="border-collapse:separate;font-family:Times"><span style="border-collapse:collapse;font-family:arial,sans-serif"><div align="left" style="font-size:13px"><div><font><span lang="ES" style="font-family:Arial">Diego Parrilla<br>
<a href="http://www.stackops.com/" title="file:///C:/Documents%20and%20Settings/carolina.capsir.per1/Application%20Data/Microsoft/Signatures/www.garrigues.com
www.garrigues.com" style="color:rgb(7,77,143)" target="_blank"><span title="file:///C:/Documents%20and%20Settings/carolina.capsir.per1/Application%20Data/Microsoft/Signatures/www.garrigues.com"></span></a></span></font><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><b>CEO</b><font size="1"><br>
</font></font><span style="border-collapse:separate;font-family:Times;font-size:medium"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"></span></span><b><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><a href="http://www.stackops.com/" target="_blank"><b>www.stackops.com</b></a> | </font></b><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><font size="1"> <a href="mailto:diego.parrilla@stackops.com" target="_blank">diego.parrilla@stackops.com</a></font></font><span style="border-collapse:separate;font-family:Times;font-size:medium"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"><font color="#004438" face="Arial"><b><b><span lang="EN-GB" style="font-size:10pt"></span></b></b></font></span></span><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><font size="1"> | </font></font><span style="border-collapse:separate;font-family:Times;font-size:medium"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><font size="1"><a href="tel:%2B34%20649%2094%2043%2029" value="+34649944329" target="_blank">+34 649 94 43 29</a> | <a>skype:diegoparrilla</a></font></font></span></span><font face="Arial" size="2" style="font-family:arial,helvetica,sans-serif"><a href="http://www.stackops.com/" target="_blank"><b><br>
</b></a></font></div></div><div style="font-size:13px"><font color="#004438" face="Arial"><b><p><span style="border-collapse:separate;font-size:medium;font-family:Times"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"><span style="border-collapse:separate;font-family:Times;font-size:medium"><span style="border-collapse:collapse;font-family:arial,sans-serif;font-size:13px"><font color="#004438" face="Arial"><b><b><span lang="EN-GB" style="font-size:10pt"><img></span></b></b></font></span></span></span></span></p>
</b></font></div></span></span><div><div><div><br></div><br>
<br><br><div class="gmail_quote">On Fri, Sep 21, 2012 at 4:39 PM, Samuel Winchenbach <span dir="ltr"><<a href="mailto:swinchen@gmail.com" target="_blank">swinchen@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi All,<br>
<br>
What are some "best practices" when it comes to overselling RAM in a<br>
KVM based openstack setup? For example:<br>
<br>
I have 4 nodes with 16 cores & 128 GB RAM each. If on one of those<br>
nodes I oversell ram 2:1 (256 GB RAM) and the VMs actually use that<br>
much does it just start swapping out pages to disk?<br>
<br>
How do all of you handle overselling RAM?<br>
<br>
Thanks,<br>
Sam<br>
<br>
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<br></blockquote></div><br><br clear="all"><div><br></div></div></div><div class="im">-- <br>Joe Topjian<div>Systems Administrator</div><div>Cybera Inc.</div><div><br></div><div><a href="http://www.cybera.ca" target="_blank">www.cybera.ca</a></div>
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