I just refreshed my HA Deepdive page. I had it on my “to do” list for a long time but never got to it. Well it took me a couple of evenings but it’s finally done and I’m happy about it. I just hope you guys find the refresh useful and enjoy it. I also flushed all the comments on the page, if you’ve got any question don’t hesitate to ask them. I might even add a FAQ one day… who knows 🙂
Want to become a VCDX before the end of year?
Yesterday I posted an article that the required exams for the VCDX certification would be available at VMworld at discounted prices. Today Rick broke the news that VCDX Defense panels are also scheduled for VMworld.
This reminded me that I still haven’t heard from VMware on the results of my VCDX Design Exam beta. I was really hoping that I would receive my passing grade (hopeful huh?) and schedule the defense during VMworld.
Well, I called Tina (she’s so famous now!) at VMware and chatted about this. She sounded hopeful that the results would be sent out by end of business tomorrow (Friday 7/24). She also informed me that in addition to VCP and VCDX exams being available at VMworld, that VMware will also be scheduling VCDX Defense sessions during the week. Great news!
I didn’t know we were allowed to talk about it but now that the word is out… Like Rick said, design exam results will be sent really soon. VCDX Defense Panels will be scheduled before and directly after VMworld, not during as far as I know. Those who passed the exam better start preparing, good luck and maybe we will meet at one of the sessions as I will be part of the panel. For the European candidates who are not attending VMworld, panels will also be scheduled in Europe. Dates and location are still to be confirmed though.
VCDX Enterprise Administration and Design Exams available at VMworld 2009!
Jon Hall posted this info on the VMTN Communities which I wanted to share with you guys.
VMware will be providing onsite testing services at VMworld 2009. A great deal is available on the VCP exam (see my post at http://communities.vmware.com/thread/222191?tstart=0 ), but more importantly, the VCDX Enterprise Administration and Design Exams will be offered! You must be pre-authorized to take these exams, so if you are already in process to take the Enterprise Administration Exam, contact [email protected] to inquire about the availability of the exam at VMworld. You can register at Pearson VUE for the Design Exam, but again you must already be in process and have authorization from VMware to take the exam. The link for registering with Pearson for the Design Exam is http://pearsonvue.com/vmware/vmworld/ . For the Enterprise Administration Exam only, you must contact us directly.
For those who want to do the Enterprise Exam check the mock exam that has also has just been released: Enterprise Administration Mock Exam.
Dave Convery also posted about discounts for these exams, which might be a nice incentive to get you guys studying!
Re: RTFM “What I learned today – HA Split Brain”
I’m going to start with a quote from Mike’s article “What I learned today…“:
Split brain is HA situation where an ESX host becomes “orphaned” from the rest of the cluster because its primary service console network has failed. As you might know the COS network is used in the process of checking if an ESX host has suffered an untimely demise. If you fail to protect the COS network by giving vSwitch0 two NICs or by adding a 2nd COS network to say your VMotion switch, under-desired consequences can occour. Anyway, the time for detecting split brain used to be 15 seconds, for some reason this has changed to 12 seconds. I’m not 100% why, or if in fact the underlying value has changed – or that VMware has merely corrected its own documentation. You see its possible to get split brain in Vi3.5 happening if the network goes down for more than 12 seconds, but comes back up on the 13th, 14th or 15th second. I guess I will have to do some research on this one. Of course, the duration can be changed – and split brain is trivial matter if you take the neccessary network redundency steps…
I thought this issue was something that was common knowledge but if Mike doesn’t know about it my guess is that most of you don’t know about this. Before we dive into Mike’s article, technically this is not a split brain, it is an “orphaned vm” but not a scenario where the disk files and the in memory VM are split between hosts.
Before we start this setting is key in Mike’s example:
das.failuredetectiontime = This is the time period when a host has received no heartbeats from another host, that it waits before declaring the other host dead.
The default value is 15 seconds. In other words the host will be declared dead on the fifteenth second and a restart will be initiated by one of the primary hosts.
For now let’s assume the isolation response is “power off”. These VMs can only be restarted if the current VMs have been powered off. Here’s the clue, the “power off”(isolation response) will be initiated by the isolated host 2 seconds before the das.failuredetectiontime.
Does this mean that you can end up with your VMs being down and HA not restarting them?
Yes, when the heartbeat returns between the 13th and 15th second shutdown could already have been initiated. The restart however will not be initiated because the heartbeat indicates that the host is not isolated.
How can you avoid this?
Pick “Leave VM powered on” as an isolation response. Increasing the das.failuredetectiontime will also decrease the chances of running in to issues like these.
Did this change?
No, it’s been like this since it has been introduced.
Whitepaper: VMware vNetwork Distributed Switch
I just noticed this great whitepaper on the Distributed Switch(vDS) and thought it might also be useful for you guys:
http://vmware.com/files/pdf/vsphere-vnetwork-ds-migration-configuration-wp.pdf
This guide is intended to help users understand the various scenarios and considerations for migration to the vNetwork Distributed Switch (vDS). It also includes a step-by-step guide on migration from a Standard Switch environment to a vDS environment.