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Some recent updates to HA deepdive

Duncan Epping · Apr 15, 2016 ·

Just a short post to point out that I updated the VVol section in the HA Deepdive. If you downloaded it, make sure to download the latest version. Note that I have added a version number to the intro and a changelog at the end so you can see what changes. Also, I recommend subscribing to it, as I plan to do some more updates in the upcoming months. For the update I’ve been playing with a Nimble (virtual) array all day today and it allowed me to create some cool screenshots of how HA works in a VVol environment. I was also seriously impressed by how easy it was to setup the Nimble (virtual) array and how simple VVol was to configure for them. Not just that, but the number of policy options Nimble exposes, I was amazed. Below is just an example of some of the things you can configure!

The screenshot below shows the Virtual Volumes created for a VM, this is the view from a Storage perspective:

vSphere HA deepdive 6.x available for free!

Duncan Epping · Feb 18, 2016 ·

I’ve been discussing this over the last 12 months with Frank, and to be honest we are still not sure what is the right thing to do but we decided to take this step anyway. Over the past couple of years we released various updates of the vSphere Clustering Deepdive. Updating the book sometimes was a massive pain (version 4 to 5 for instance), but some of the minor updates have been relative straight forward, although still time consuming due to formatting / diagrams / screenshots etc.

Ever since we’ve been looking for new ways to distribute our book, or publication as I will refer to it from now on. I’ve looked at various options, and found one which I felt was the best of all worlds: Gitbook. Gitbook is a solution which allows you as an author to develop content in Markdown and distribute it in various different formats. This could be as static html, pdf, ePub or Mobi. Basically any format you would want in this day and age. The great thing about the platform as well is that it integrates with Github and you can share your source there and do things like version control etc. It does it in such a way that I can use the Gitbook client on my Mac, while someone else who wants to contribute or submit a change can simply use their client of choice and submit a change through git. Although I don’t expect too many people to do this, it will make it easier for me to have material reviewed for instance by one of the VMware engineers.

So what did I just make available for free? Well in short, an updated version (vSphere 6.0 Update 1) of the vSphere HA Deepdive. This includes the stretched clustering section of the book. Note that DRS and SDRS have not been included (yet). This may or may not happen in some shape or form in the future though. For now, I hope you will enjoy and appreciate the content that I made available for free. You can access it by clicking “HA Deepdive” on the left, or (in my opinion) for a better reading experience read it on Gitbook directly through this link: ha.yellow-bricks.com.

Note that there are links as well to download the content in different formats, for those who want to read it on their iPad / phone / whatever. Also note that Gitbook allows you to comment on a paragraph by clicking the “+” sign on the right side of the paragraph when you hover over it… Please submit feedback when you see mistakes! And for those who are really active, if you want to you could even contribute to the content! I will keep updating the content over the upcoming months probably with more info on VVols and for instance the Advanced Settings, so keep checking back regularly!

HA/DRS configuration with Virtual SAN Stretched Cluster environment

Duncan Epping · Sep 9, 2015 ·

This question is going to come sooner or later, how do I configure HA/DRS when I am running a Virtual SAN Stretched cluster configuration. I described some of the basics of Virtual SAN stretched clustering in a what’s new for 6.1 post already, if you haven’t read it then I urge you to do so first. There are a couple of key things to know, first of all the latency between data sites that can be tolerated is 5ms and to the witness location ~100ms.

If you look at the picture you below you can imagine that when a VM sits in Fault Domain A and is reading from Fault Domain B that it could incur a latency of 5ms for each read IO. From a performance perspective we would like to avoid this 5ms latency, so for stretched clusters we introduce the concept of read locality. We don’t have this in a non-stretched environment, as there the latency is microseconds and not miliseconds. Now this “read locality” is something we need to take in to consideration when we configure HA and DRS.

Using VM-Host rules without DRS enabled

Duncan Epping · Aug 20, 2015 ·

This week I was playing with the VM-Host rules in my environment. In this particular environment I had DRS disabled and I noticed some strange things when I created the VM-Host rules. I figured it should all work in a normal way as I was always told that VM/Host rules can be configured without DRS being enabled. And from a “configuration” perspective that is correct. However there is a big caveat here, and lets look at the two options you have when creating a rule namely “should” and “must”.

When using a VM-Host “must” rule when DRS is disabled it all works as expected. When you have the rule defined then you cannot place the VM on a host which is not within the VM-Host group. You cannot power it on on those hosts, no vMotion and HA will not place the VM there either after a failure. Everything as expected.

In the case of a VM-Host “should” rule when DRS is disabled this is different! When you have a should rule defined and DRS is disabled then vCenter will allow you to power on a VM on a host which is not part of the rule. HA will restart VMs on hosts as well which are not part of the rule, and you can migrate a VM to one of those hosts. All of this without a warning that the host is not in the rule and that you are violating the rule. Even after explicitly defining an alarm I don’t see anything triggered. The alarm by the way is called “VM is violating a DRS VM-Host affinity rule”.

I reached out to the HA/DRS engineering team and asked them why that is. It appears the logic for the “should” rule, in contrary to the “must rule, is handled by DRS. This includes the alerting. It makes sense to a certain extent, but it wasn’t what I expected. So be warned, if you don’t have DRS enabled, “VM-Host should rules” will not work. Must rules however will work perfectly fine. (Yes, I’ve asked them to look in to this and fix it so it behaves as you would expect it to behave and come with a warning when you try anything that violates a should rule.)

Conservative vs Aggressive for VMCP APD response

Duncan Epping · Jun 19, 2015 ·

I just finished writing the vMSC 6.0 Best Practices paper which is about to be released when a question came in. The question was around the APD scenario and whether the response to an APD should be set to aggressive or conservative. Its a good question and my instinct immediately say: conservative… But should it be configured to that in all cases? If so, why on earth do we even have an aggressive method? That got me thinking. (By the way, make sure to read this article by Matt Meyer on VMCP on the vSphere blog, good post!) But before I spill the beans, what is aggressive/conservative in this case, and what is this feature again?

VM Component Protection (VMCP) is new in 6.0 and it allows vSphere to respond to a scenario where the host has lost access to a storage device. (Both PDL and APD.) In previous releases, vSphere was already capable of responding to PDL scenarios but the settings weren’t really exposed in the UI and that has been done with 6.0 and the APD response has also been added at the same time. Great feature if you ask me, especially in stretched environments as it will help during certain failure scenarios. [Read more…] about Conservative vs Aggressive for VMCP APD response