<html><body><div style="font-family: times new roman, new york, times, serif; font-size: 12pt; color: #000000"><div></div><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>From: </b>"ml ml" <mliebherr99@googlemail.com><br><b>To: </b>Users@ovirt.org<br><b>Sent: </b>Wednesday, February 5, 2014 12:45:55 PM<br><b>Subject: </b>[Users] Will this two node concept scale and work?<br><div><br></div><div dir="ltr"><div>Hello List,<br><div><br></div></div><div>my aim is to host multiple <span style="background:none repeat scroll 0% 0% yellow" class="">VMs</span> which are redundant and are high available. It should also scale well.<br><div><br></div></div><div>I think usually people just buy a fat <span style="background:none repeat scroll 0% 0% yellow" class="">iSCSI</span> Storage and attach this. In my case it should scale well from very small nodes to big ones.<br></div><div>Therefore an <span style="background:none repeat scroll 0% 0% yellow" class="">iSCSI</span> Target will bring a lot of overhead (10GBit Links and two Paths, and really i should have a 2nd Hot Standby SAN, too). This makes scalability very hard.<br><div><br></div>This post is also not meant to be a <span style="background:none repeat scroll 0% 0% yellow" class="">iscsi</span> discussion.<br><div><br></div></div><div>Since <span style="background:none repeat scroll 0% 0% yellow" class="">oVirt</span> does not support <span style="background:none repeat scroll 0% 0% yellow" class="">DRBD</span> out of the box i came up with my own concept:<br></div><div><br><a href="http://oi62" target="_blank">http://oi62</a>.<span style="background:none repeat scroll 0% 0% yellow" class="">tinypic</span>.com/2550xg5.<span style="background:none repeat scroll 0% 0% yellow" class="">jpg</span><br><div><br></div></div><div>As far as i can tell i have the following advantages:<br></div><div>--------------------------------------------------------------------<br>- i can start with two simple cheap nodes<br></div><div>- i could add more disks to my nodes. Maybe even a <span style="background:none repeat scroll 0% 0% yellow" class="">SSD</span> as a dedicated <span style="background:none repeat scroll 0% 0% yellow" class="">drbd</span> resource.<br></div><div>- i can connect the two nodes directly to each other with bonding or <span style="background:none repeat scroll 0% 0% yellow" class="">infiniband</span>. i <span style="background:none repeat scroll 0% 0% yellow" class="">dont</span> need a switch or something between it.<br><div><br></div></div><div>Downside:<br>---------------<br></div><div>- i always need two nodes (as a couple)<br><div><br></div></div><div>Will this setup work for me. So far i think i will be quite happy with it.<br></div><div>Since the <span style="background:none repeat scroll 0% 0% yellow" class="">DRBD</span> Resources are shared in dual primary mode i am not sure if <span style="background:none repeat scroll 0% 0% yellow" class="">ovirt</span> can handle it. It is not allowed to write to a <span style="background:none repeat scroll 0% 0% yellow" class="">vm</span> disk at the same time.</div></div></blockquote><div><br></div><div>I don't know ovirt enough to comment on that.</div><div><br></div><div>I did play in the past with drbd and libvirt (virsh).</div><div>Note that having both nodes primary all the time for all resources is</div><div> calling for a disaster. In any case of split brain, for any reason, drbd</div><div> will not know what to do.</div><div><br></div><div>What I did was to allow both to be primary, but had only one primary</div><div> most of the time (per resource). I wrote a script to do migration, which</div><div> made both primary for the duration of the migration (required by qemu)</div><div> and then moved the source to secondary when migration finished. This</div><div> way you still have a chance for a disaster, if there is a problem (split</div><div> brain, node failure) during a migration. So if you decide to go this way,</div><div> carefully plan and test to see that it works well for you. <span style="font-size: 12pt;">One source for</span></div><div><span style="font-size: 12pt;"> a split brain, for me, at the time, was buggy nic drivers </span><span style="font-size: 12pt;">and bad bonding</span></div><div><span style="font-size: 12pt;"> configuration. So test that well too if applicable.</span></div><div><span style="font-size: 12pt;"><br></span></div><div><span style="font-size: 12pt;" data-mce-style="font-size: 12pt;"><span style="font-size: 12pt;" data-mce-style="font-size: 12pt;"><span style="font-size: 12pt;" data-mce-style="font-size: 12pt;">The approach I took seems similar to "<span style="background-color: rgb(255, 255, 255); color: rgb(85, 87, 83); font-family: 'Venturis Sans', 'Open Sans', sans-serif; font-size: 14px; line-height: 20px;">DRBD on LV level</span></span></span></span><span style="font-size: 12pt;" data-mce-style="font-size: 12pt;"><span style="font-size: 12pt;" data-mce-style="font-size: 12pt;">" in [1], but</span></span></div><div><span style="font-size: 12pt;" data-mce-style="font-size: 12pt;"><span style="font-size: 12pt;" data-mce-style="font-size: 12pt;">with custom scripts and without ovirt.</span></span></div><div><br></div><div>You might be able to make ovirt do this for you with hooks. Didn't try that.</div><div><br></div><div>An obvious downside to this approach is that if one node in a pair is</div><div> down, the other has no backup now. If you have multiple nodes and</div><div> external <span style="font-size: 12pt;">shared storage, multiple nodes can be down with no disruption</span></div><div><span style="font-size: 12pt;"> to service </span><span style="font-size: 12pt;">if the remaining nodes are capable enough.</span></div><div><br></div><div>[1] <a href="http://www.ovirt.org/Features/DRBD">http://www.ovirt.org/Features/DRBD</a><a href="http://www.ovirt.org/Features/DRBD" data-mce-href="http://www.ovirt.org/Features/DRBD"></a></div><div><br></div><div>Best regards,</div><div>-- <br></div><div><span name="x"></span>Didi<span name="x"></span><br></div><div><br></div></div></body></html>