Yellow Bricks

by Duncan Epping

4.1

PowerCLI Reference Book, the review

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I was checking Amazon during the weekend, just like I do everyday, to see if we had new reviews and how the book was selling until I noticed the reviews on the PowerCLI book. The reviews were mainly about the fact that there’s a formatting issue with the ebook which I agree with should be fixed by the publisher but rating it with a 3 / 4 stars just doesn’t cut it in my opinion. Here’s my review of the book, please note that I know the authors really well and they gave me a free copy nevertheless I have been completely honest about what I think about the book. If I would think it was crap I would let you know, before I copy/paste the review here I would like to ask the Authors to pressure their publisher to lower the price of the ebook as right now it is more expensive than the paper version which is just nonsense. Mr or Mrs Sybex, it is time to change your strategy.

Anyway, I gave the PowerCLI Reference Book 5 stars as I truly believe it is one of a kind, here’s my justification for it:

I received the paper-version of the book last week and started reading it straight away. The authors are THE number one PowerCLI experts in the world and take you through the trenches of vSphere automation.
Although I know vSphere inside out I am a novice when it comes to PowerCLI. The main reason being that I never gave myself the time to actually learn PowerCLI as I figured I could do things faster using the UI. Although this might be true in some cases the first thing the book tought me was that my perception was wrong. The book shows you how to optimize your day-to-day operations by taking advantage of what PowerCLI has to offer out of the box, but it also teaches you how to create your own functions. The amount of examples in there in terms of PowerCLI scripts are such a valuable asset that I would highly recommend it to anyone who is interested in learning PowerCLI and/or optimizing their operational procedures. We are not talking about reporting only, for instance configuring vSwitches or restricting the amount of snapshots is all shown in this book. Be warned though, don’t expect a step-by-step Learning PowerCLI Guide, this is 700+ pages of pure PowerCLI automation at its best which will enable you to get the most out of your environment.

Not included on Amazon, but I do feel it would have been nice if the structure of the book was slightly different. I would have personally started with an Introduction chapter, followed “in-box” reporting functionality and finishing it off with deepdive functions and pages of script. But than again, this is a reference book and not course material. All in all, this book is more than worth it.

You can buy it here if you are interested.
(yes it contains an affiliate link)

Mythbusters: ESX/ESXi caching I/O?

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We had a discussion internally about ESX/ESXi caching I/Os. In particular this discussion was around caching of writes  as a customer was concerned about consistency of their data. I fully understand that they are concerned and I know in the past some vendors were doing write caching however VMware does not do this for obvious reasons. Although performance is important it is worthless when your data is corrupt / inconsistent. Of course I looked around for  data to back this claim up and bust this myth once and for all. I found a KB article that acknowledges this and have a quote from one of our VMFS engineers.

Source Satyam Vaghani (VMware Engineering)
ESX(i) does not cache guest OS writes. This gives a VM the same crash consistency as a physical machine: i.e. a write that was issued by the guest OS and acknowledged as successful by the hypervisor is guaranteed to be on disk at the time of acknowledgement. In other words, there is no write cache on ESX to talk about, and so disabling it is moot. So that’s one thing out of our way.

Source – Knowledge Base
VMware ESX acknowledges a write or read to a guest operating system only after that write or read is acknowledged by the hardware controller to ESX. Applications running inside virtual machines on ESX are afforded the same crash consistency guarantees as applications running on physical machines or physical disk controllers.

What? An ebook? Is this a late April Fools’ joke?

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No it isn’t a late April Fools’ joke… And we never expected this to actually happen to be honest. Last week I had discussion about the ebook on twitter and people were convinced that ebooks are the way to go. I won’t deny that and I know Frank agrees with me on this as well but the fact of the matter is that we just didn’t have the time to do all the reformatting work. I asked once again on twitter if someone knew any tools that we could leverage or if someone could give us a hand. The last 4 times I asked this question no one responded and again hardly anyone did, however a close relative of mine did contact me and told me he had some tools that could possibly help us. I forwarded the PDF and the DOCX file and within a couple of hours I received an almost clean .html file back. The email also contained a very important tip, Mobipocket Creator. So I installed it and added the html file to it and clicked “Convert”….

Yes it was close, but not close enough to be published yet. I shared the book with Frank and both of us opened it up in our Kindle App and reviewed the layout. We marked all the pages that had some glitches and started editing those. We expected to be done in a couple of hours but it ended up being a full day again for both of us… but who cares the result is worth it.

After doing research on the Kindle Store we had another decision to make; pricing. We noticed that some ebooks are more expensive than the paper version, WHAT? We didn’t want to do that. We never expected to release this and every copy sold is an extra copy sold of our book and we know that many who wanted the ebook bought the paper version instead so we decided to make it cheap, almost half the price of the cheapest vSphere book on the list (calling all publishers, revisit your pricing strategy!) and $ 17.45 less than the paper version.

But before we give you the link, one of the most asked questions… Why Kindle? Well Kindle happens to be a multi-platform solution. The Kindle Application is available for Mac, Windows, iPad, Android, Blackberry, Windows Phone 7. Which made us believe that if we had to pick one format Kindle was the way to go.

So without further ado we present: vSphere 4.1 HA and DRS technical deepdive, the ebook…… for only $ 7.50. Pick it up,

Frank & Duncan
ps: it is also available in the UK Kindle Store for £5.36.

das.failuredetection time and the isolation response

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I had a discussion on the VMTN forums about this last week and the question basically was, what should my das.failuredetection time be set to when the isolation response is set to “Shut down”.

Lets first explain what the das.failuredetectiontime is, I described it on our book as follows:

Failure Detection Time is basically the time it takes before the “isolation response” is triggered. There are two primary concepts when we are talking about failure detection time:

  • The time it will take the host to detect it is isolated
  • The time it will take the non-isolated hosts to mark the unavailable host as isolated and initiate the failover

So what does this have to do with your Isolation Response? Well not much actually, and that might sound weird but it had me thinking about it for a second as well….

What if your Isolation Response is set to “Shut down” and an isolation occurs? Well in that case HA will try to “Shut down” the VMs in a clean way when Isolation has been detected. HA will do that on the 14th second. On the 16th second the restart will be initiated. So that leaves your VMs exactly two second to shut down in a clean way….So two questions pop-up immediately:

  1. What if I increase the das.failuredetectiontime?
  2. What are the chances restarts happens in time?

Increasing the das.failuredetectiontime wouldn’t make a difference as the “2 second” gap will just move up as well. HA will always ping the isolation address on “das.failuredetectiontime – 1” and it will always initiate the restarts on “das.failuredetection + 1”. In other words, 2 minutes or 20 seconds, it makes no difference. I guess a nice diagram makes this a bit clearer:

(created by Frank D. for our book)

So what are the chances these restarts will occur within 16 seconds? Slim indeed. So when will they be restarted? Well a year ago I wrote this article and the following still applies for vSphere 4.1:

  • T+0 – Restart
  • T+2 – Restart retry 1
  • T+4 – Restart retry 2
  • T+8 – Restart retry 3
  • T+8 – Restart retry 4
  • T+8 – Restart retry 5

In other words, if T+0 fails the restart will be retried 2 minutes later. If that one fails the restart will be retried 4 minutes later. (2+4 = 6 minutes after the initial restart) So as you can see selecting “shut down” will more than likely increase your restart latency and this needs to be taken into account for your SLA.

Virtual Machine Storage and Snapshots Survey

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It seems to be survey month…. Nevertheless this survey will take you a couple of minutes and is about Virtual Machine Storage and Snapshots. Most of our PMs are currently revising / updating and prioritizing the roadmap and real customer data and opinions are always welcome to define these. We would appreciate it if you could take 5 minutes of your time to complete this one, it is 12 questions.

Virtual Machine Storage and Snapshots Survey