Yellow Bricks

by Duncan Epping

6.7

What happened to MaxCostPerEsx41DS? It doesn’t seem to work in vSphere 6.x?

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Today I received a question which also caught me by surprise, someone updated from vSphere 5.0 and he noticed that when doing an SDRS Maintenance Mode that the setting MaxCostPerEsx41DS did not work. This setting actually limits the number of active SvMotions on a single datastore. You can imagine that this can be desired when you are “limited” in terms of performance. I was a bit surprised as I had not heard that these settings changed at all. Also, a quick search on internal pages and externally did not deliver any results. After a discussion with some support folks and some more digging, I found a reference to a naming change. Not surprising I guess, but as per vSphere 6.0 the setting is called MaxCostPerEsx6xDS. So if you would like to limit the number of SvMotion’s active at the same time, please note the change in names.

For more background on this topic I would like to refer to Frank’s excellent blog on this topic here.

You asked for it: vSphere 6.7 Clustering Deep Dive ebook, now available!

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We knew when we released the paper version of the book that many would yell: What about an e-book? Although sales numbers of the Host Deep Dive and previous Clustering Deep Dive books have shown that by far most people prefer a printed copy, we decided to go ahead and create an ebook as well. It is not as simple unfortunately as simply uploading a PDF or an MS Word file. We had to spend evenings reformatting the book in an e-book authoring tool, compile it, review it, fix issues, compile again etc. Nevertheless, it is done!

So what we did is we just uploaded it to Amazon, and we made it available for 14,95 USD, or whatever that roughly converts to in your local currency in your local store. We also noticed there was a bundling option, so as soon as the ebook and the paper copy are linked you can buy the ebook alongside the paper copy for only 2,99 USD. (Linking the book may still take a couple of days, we’ve initiated the process with Amazon and are waiting for them to complete it.)

You wanted it, so go out and pick it up, right before the weekend! Also, note that we have both the ebook and the paper version available right now, we are working on linking the books, so you can get a nice deal for both versions. Also, I would highly recommend picking up the Host Deep Dive books as well, and while you are at it pick up the VDI guide, it is an excellent read! Amazon links are on the right side for your convenience.

Now Available: vSphere 6.7 Clustering Deep Dive book!

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Over the past couple of months Frank, Niels and I have worked ferociously to update the vSphere Clustering Deep Dive. Some of the material was already brought up to date to vSphere 6.0 U2, but the majority was never updated after vSphere 5.1. As you can imagine, this was a tremendous undertaking. Not only did we need to validate every sentence, all diagrams needed to be updated, and with the introduction of the HTML-5 Client also all screenshots had to be retaken. 

Now, just a couple of weeks before VMworld, we are finally at the point where we can press “publish”.

What can you expect? Well, we have said this with previous books, this is not a beginners guide! This is a deep dive, and we aimed to take you in to the trenches of vSphere Clustering technologies. We cover a multitude of different features, and for those who haven’t read the previous books expect the following features to be covered:

  • vSphere HA
  • vSphere DRS
  • vSphere Storage DRS
  • vSphere Storage I/O Control
  • vSphere Network I/O Control

We also have a chapter on stretched clusters, in this chapter we describe how to design and implement a vSphere Metro Storage Cluster, leveraging all of the knowledge gained in the previous chapters.

For your convenience, I copied/pasted some of the Amazon info below.

—

  • Paperback: 566 pages
  • Publisher: CreateSpace Independent Publishing Platform; 1 edition (July 29, 2018)
  • Language: English
  • ISBN-10: 1722625325
  • ISBN-13: 978-1722625320
  • Product Dimensions: 5.5 x 1.3 x 8.5 inches
  • Shipping Weight: 1.8 pounds

—

I hope all of you will enjoy the book as much as we enjoyed writing it. And before I forget, I want to thank my co-authors for the late night discussions, the hard work, insights and fun/laughter at times.

Get it while it is hot! (Look on the right side column for the links to the book!)

Insufficient configured resources to satisfy the desired vSphere HA failover level on the cluster

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I was talking to the HA team this week, specifically about the upcoming HA book. One thing they mentioned is that people still seem to struggle with the concept of admission control. This is the reason I wrote a whole chapter on it years ago, yet there still seems to be a lot of confusion. One thing that is not clear to people is the percentage calculations. We have some customers with VMs with extremely large reservations, in that case instead of using the “slot policy” they typically switch to “percentage based policy”. Simply as the percentage based policy is a lot more flexible.

However, recently we have had some customers that hit the following error message:

Insufficient configured resources to satisfy the desired vSphere HA failover level on the cluster

This error message, in the case of these particular situations (yes there was a bug as well, read this article on that), set the percentage lower than what would equal a full host. In other words, in a 4 host environment, a single host would equal 25%. In some cases, customers would set the percentage to a value lower than 25%. I am personally not sure why anyone would do this as it contradicts the whole essence of admission control. Nevertheless, it happens.

This message indicates that you may not have sufficient resources, in the case of a host failure, to restart all the VMs. This of course is the result of the percentage being set lower than the value that would equal a single host. Note though, this does not stop you from powering on new VMs. You will only be stopped from powering on new VMs when you exceed the available unreserved resources.

So if you are seeing this error message, please verify the configured percentage if you set it manually. Ensure that at a minimum it equals the largest host in the cluster.

** back to finalizing the book **

 

Trigger APD on iSCSI LUN on vSphere

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I was testing various failure scenarios in my lab today for the vSphere Clustering Deepdive session I have scheduled for VMworld. I needed some screenshots and log files of when a datastore hit an APD scenario, for those who don’t know APD stands for all paths down. In other words: the storage is inaccessible and ESXi doesn’t know what has happened and why. vSphere HA has the ability to respond to that kind of failure. I wanted to test this, but my setup was fairly simple and virtual. So I couldn’t unplug any cables. I also couldn’t make configuration changes to the iSCSI array as that would rather trigger a PDL (permanent device loss), so how do you test and APD scenario?

After trying various things like killing the iSCSI daemon (it gets restarted automatically with no impact on the workload) I bumped in to this command which triggered the APD:

  • SSH in to the host you want to trigger the APD on, run the following command 
    esxcli iscsi session remove  -A vmhba65
  • Make sure of course to replace “vmhba65” with the name of your iSCSI adapter

This triggered APD, as witness in the fdm.log and vmkernel.log, and ultimately resulted in vSphere HA killing the impacted VM and restarting it on a healthy host. Anyway, just wanted to share this as I am sure there are others who would like to test APD responses in their labs or before their environment goes in to production.

There may be other easy ways as well, if you know any, please share in the comments section.