<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Verdana;
panose-1:2 11 6 4 3 5 4 4 2 4;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
p
{mso-style-priority:99;
mso-margin-top-alt:auto;
margin-right:0in;
mso-margin-bottom-alt:auto;
margin-left:0in;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
pre
{mso-style-priority:99;
mso-style-link:"HTML Preformatted Char";
margin:0in;
margin-bottom:.0001pt;
font-size:10.0pt;
font-family:"Courier New";}
p.MsoListParagraph, li.MsoListParagraph, div.MsoListParagraph
{mso-style-priority:34;
margin-top:0in;
margin-right:0in;
margin-bottom:0in;
margin-left:.5in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
span.HTMLPreformattedChar
{mso-style-name:"HTML Preformatted Char";
mso-style-priority:99;
mso-style-link:"HTML Preformatted";
font-family:Consolas;}
p.msonormal0, li.msonormal0, div.msonormal0
{mso-style-name:msonormal;
mso-style-priority:99;
mso-margin-top-alt:auto;
margin-right:0in;
mso-margin-bottom-alt:auto;
margin-left:0in;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
span.EmailStyle22
{mso-style-type:personal;
font-family:"Calibri",sans-serif;
color:#1F497D;}
span.EmailStyle23
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
/* List Definitions */
@list l0
{mso-list-id:1793280372;
mso-list-type:hybrid;
mso-list-template-ids:1040718426 67698703 67698713 67698715 67698703 67698713 67698715 67698703 67698713 67698715;}
@list l0:level1
{mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level2
{mso-level-number-format:alpha-lower;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level3
{mso-level-number-format:roman-lower;
mso-level-tab-stop:none;
mso-level-number-position:right;
text-indent:-9.0pt;}
@list l0:level4
{mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level5
{mso-level-number-format:alpha-lower;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level6
{mso-level-number-format:roman-lower;
mso-level-tab-stop:none;
mso-level-number-position:right;
text-indent:-9.0pt;}
@list l0:level7
{mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level8
{mso-level-number-format:alpha-lower;
mso-level-tab-stop:none;
mso-level-number-position:left;
text-indent:-.25in;}
@list l0:level9
{mso-level-number-format:roman-lower;
mso-level-tab-stop:none;
mso-level-number-position:right;
text-indent:-9.0pt;}
ol
{margin-bottom:0in;}
ul
{margin-bottom:0in;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Hi Leo,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">We use VMs for Spectrum Scale all of the time (including VM-based NAS clusters that span multiple sites) and all of the cloud-based offerings do as well, so it’s
pretty clearly a thing that people are using. (Note: all of my experience is on Ethernet fabrics, so keep that in mind when I’m discussing networking.) But you’re right that there are a few pitfalls, such as…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Licensing. The traditional PVU license model discouraged adding machines to clusters and encouraged the concentration of server roles in a way that
didn’t align with best practices. If you’re on capacity based licensing then this issue is moot. (We’ve been in that model for ages, and so consequently we have years of experience with GPFS and VMs. But with PVUs we probably wouldn’t have gone this way.)
<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Virtualized networking can be flaky. In particular, I’ve found SR-IOV to be unreliable. Suddenly in the middle of a TCP session you might see GPFS
complain about “Unexpected data in message. Header dump: cccccccc cccc cccc…” from a VM whose virtual network interface has gone awry and necessitates a reboot, and which can leave corrupted data on disk when this happens, requiring you to offline mmfsck and/or
spelunk through a damaged filesystem and backups to recover. Based on this, I would recommend the following:<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo2">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">a.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Do NOT use SR-IOV. If you’re using KVM then just stick with virtio (vnet and bridge interfaces).<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo2">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">b.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">DO enable all of the checksum protection you can get on the cluster (e.g. nsdCksumTraditional=yes). This can act as a backstop against network reliability
issues and in practice on modern machines doesn’t appear to be as big of a performance hit as it once was. (I’d recommend this for everyone honestly.)<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo2">
<![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">c.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Think about increasing your replication factor if you’re running filesystems with only one copy of data/metadata. One of the strengths of GPFS is its
support for replication, both as a throughput scaling mechanism and for redundancy, and that redundancy can buy you a lot of forgiveness if things go wrong.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Sizing. Do not be too stingy with RAM and CPU allocations for your guest nodes. Scale is excellent at multithreading for things like parallel inode
scan, prefetching, etc, and remember that your quorum nodes will be token managers by default unless you assign the manager roles elsewhere, and may need to have enough RAM to support their share of the token serving workload. A stable cluster is one in which
the servers aren’t thrashing for a lack of resources.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Others may have additional experience and best practices to share, which would be great since I don’t see this trend going away any time soon.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Good luck,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Paul<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> gpfsug-discuss-bounces@spectrumscale.org <gpfsug-discuss-bounces@spectrumscale.org>
<b>On Behalf Of </b>Leonardo Sala<br>
<b>Sent:</b> Monday, June 7, 2021 08:47<br>
<b>To:</b> gpfsug-discuss@spectrumscale.org<br>
<b>Subject:</b> [gpfsug-discuss] Using VMs as quorum / admin nodes in a GPFS infiniband cluster<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p><span style="font-size:9.0pt;font-family:"Verdana",sans-serif;color:#CC0000">This message was sent by an external party.<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p><span style="font-family:"Courier New"">Hallo,</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">we do have multiple bare-metal GPFS clusters with infiniband fabric, and I am actually considering adding some VMs in the mix, to perform admin tasks (so that the bare metal servers do not need passwordless ssh keys)
and quorum nodes. Has anybody tried this? What could be the drawbacks / issues at GPFS level?</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">Thanks a lot for the insights!</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">cheers</span><o:p></o:p></p>
<p><span style="font-family:"Courier New"">leo</span><o:p></o:p></p>
<pre>-- <o:p></o:p></pre>
<pre>Paul Scherrer Institut<o:p></o:p></pre>
<pre>Dr. Leonardo Sala<o:p></o:p></pre>
<pre>Group Leader High Performance Computing<o:p></o:p></pre>
<pre>Deputy Section Head Science IT<o:p></o:p></pre>
<pre>Science IT<o:p></o:p></pre>
<pre>WHGA/036<o:p></o:p></pre>
<pre>Forschungstrasse 111<o:p></o:p></pre>
<pre>5232 Villigen PSI<o:p></o:p></pre>
<pre>Switzerland<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>Phone: +41 56 310 3369<o:p></o:p></pre>
<pre><a href="mailto:leonardo.sala@psi.ch">leonardo.sala@psi.ch</a><o:p></o:p></pre>
<pre><a href="http://www.psi.ch">www.psi.ch</a><o:p></o:p></pre>
</div>
</div>
</body>
</html>