by Duncan Epping
The question “How to remove a host from your Virtual SAN cluster” has now popped up various times, so I figured I would write a short article around what the current procedure is. It is fairly straight forward to be honest, here we go:
That is it, now you can re-purpose the host for anything else.
I have had this problem various times in the last 6 months on my WordPress blog. For whatever reason all of a sudden when I access my wp-admin page I receive an access denied on wp-admin / wp-login.php. Really annoying as you can imagine as it means you cannot get in to the back-end of your blog making it impossible to manage it. The blog it self is still available though when this happens so I figured I would write down the fix, as I somehow keep forgetting it.
Simple solution, for a strange problem. If I ever find the rootcause I will post it here as well.
Yeah that title got your attention right… For now it is just me writing about it and nothing has been announced or promised. At VMworld I believe it was Intel who demonstrated the possibilities in this space, an All Flash Virtual SAN. A couple of weeks back during my holiday someone pointed me to a couple of articles which were around SSD endurance. Typically these types of articles deal with the upper-end of the spectrum and as such are irrelevant to most of us, and some of the articles I have read in the past around endurance were disappointing to be honest.
TechReport.com however decided to look at consumer grade SSDs. We are talking about SSDs like the Intel 335, Samsung 840 series, Kingston Hyper-X and the Corsair Neutron. All of the SSDs used had a capacity of around 250GB and are priced anywhere between $175 and $275. Now if you look at the guarantees given in terms of endurance, we are talking about anything ranging from “20GB of writes per day for the length of its three-year warranty” for the Intel (22TB in total) to three-year and 192TB in total for the Kingston, and anything in between for the other SSDs.
Tech Report had set their first checkpoint at 22TB. After running through a series of tests, which are described in the article, they compare the results between the various SSDs after 22TB writes. Great to see that all SSDs did what they are supposed to do and promised. All of them passed the 22TB mark without any issues. They had another checkpoint at the 200TB mark, which showed the first signs of weakness. As expected the lower end SSDs dropped out first. The next checkpoint was set at the 300TB mark, they also added an unpowered retention test to see how well they retain data when unplugged. So far impressive results, and a blog series I will follow with interest. The articles clearly show that from an endurance perspective the SSDs perform a lot better than most had assumed in the past years. It is fair to say that the consumer grade SSDs are up to the challenge.
Considering the low price points of these flash devices, I can see how an All Flash Virtual SAN solution would be possible leveraging these consumer grade SSDs as the capacity tier (reads) and using enterprise grade SSDs to provide write performance (write buffer). Hopefully we will start to see the capacity increase even further of these types of devices, today some of them go up to 500GB others up to 800GB, wouldn’t it be nice to have a 1TB (or more) version?
Anyway, I am excited and definitely planning on running some test with an all flash Virtual SAN solution in the future… What about you?
** 500TB blog update! **
** 600TB blog update! **
** 1PB blog update! **
** 2PB blog update **
** Conclusion **
I have had this question so many times I figured I would write an article about it, how to calculate what your Virtual SAN datastore size should be? Ultimate this determines which kind of server hardware you can use, which disk controller you need and which disks… So it is important that you get it right. I know the VMware Technical Marketing team is developing collateral around this topic, when that has been published I will add a link here. Lets start with a quote by Christian Dickmann one of our engineers as it is the foundation of this article:
In Virtual SAN your whole cluster acts as a hot-spare
Personally I like to work top-down, meaning that I start with an average for virtual machines or a total combined number. Lets take an example to go through the exercise, makes it a bit easier to digest.
Lets assume the average VM disk size is 50GB. On average the VMs have 4GB of memory provisioned. And we have 100 virtual machines in total that we want to run on a 4 host cluster. Based on that info the formula would look something like this:
(total number of VMs * average VM size) + (total number of VMs * average VM memory size) = total capacity required
In our case that would be:
(100 * 50GB) + (100 * 4GB) = 5400 GB
So that is it? Well not really, like every storage / file system there is some overhead and we will need to take the “failures to tolerate” in to account. If I set my “failures to tolerate” to 1 than I would have 2 copies of my VMs, this means I need 5400 GB * 2 = . Personally I also add an additional 10% in disk capacity to ensure we have room for things like: meta data, log files, vmx files and some small snapshots when required. Note that VSAN by default provisions all VMDKs as thin objects (note that swap files are thick, Cormac explained that here), so there should be room available regardless. Better safe than sorry though. This means that 10800 GB actually becomes 11880 GB. I prefer to round this up to 12TB. The formula I have been using thus looks as follows:
(((Number of VMs * Avg VM size) + (Number of VMs * Avg mem size)) * FTT+1) + 10%
Now the next step is to see how you divide that across your hosts. I mentioned we would have 4 hosts in our cluster. We have two options, we create a cluster that can re-protect itself after a full host failure or we create cluster that cannot. Just to clarify, in order to have 1 host of spare capacity available we will need to divide the total capacity by 3 instead of 4. Lets look at those two options, and what the impact is:
Now if you look at the numbers, we are talking about an additional 1TB per host. With 4 hosts, and lets assume we are using 2.5″ SAS 900GB Hitachi drives that would be 4 additional drives, at a cost of around 1000 per drive. When using 3.5″ SATA drives the cost would be a lot lower even. Although this is just a number I found on the internet it does illustrate that the cost of providing additional availability could be small. Prices could differ though depending on the server brand used. But even at double the cost, I would go for the additional drive and as such additional “hot spare capacity”.
To make life a bit easier I created a calculator. I hope this helps everyone who is looking at configuring hosts for their Virtual SAN based infrastructure.
I started reading this book by Scott Berkun titled “Confessions of a public speaker”. After the first couple of chapters I felt I wasn’t alone… What I am talking about? Stage Fright / Fear of Public Speaking. Let me start with a quote first…
Mark Twain, who made most of his income from speaking, not writing, said, “There are two types of speakers: those that are nervous and those that are liars.”
For those considering speaking at a VMUG but are terrified, I hope you find comfort in knowing that the majority of people you see presenting at these events have (or had) similar feelings. I don’t know anyone who is not nervous when he goes up on stage. Those who say they are not probably indeed lie about it, yes there are some exceptions to the rule of course as always, but I can tell you that I am not one of those. I used to be terrified, stage fright is the right word.
Just to speak from my own experience, a lot of people seem to think that presenting is part of my role and is something I enjoy doing. I do enjoy it when the session is over, but the journey there I don’t enjoy. I am still nervous when I go up on stage, and depending on the size that is either nervous/excited or nervous/scared. Yes, like many of you reading this, the first couple of times presenting I wondered WHY am I doing this? It was painful being up on stage, it was painful doing dry-runs, and it even felt crap afterwards. WHY am I doing this?
Personally I believe I need to place myself in an uncomfortable situation to grow / learn. This applies to learning new skills, like public speaking, but also broadening the horizon from a job/career perspective. You can be a “virtualization admin” for the rest of your life and do it with your eyes closed… You can also take on a completely new set of responsibilities, yes you will feel uncomfortable for a couple of weeks or even months, but guess what after a while it all feels like you have been doing it for years… Same applies to public speaking, only way to get comfortable with that fear or nervous feeling is by doing it!
So what are some of the mistakes I made, and probably still make every once in a while, and what should you be doing or not doing?
Practice while you build your deck… I do this regularly to test the flow and see if the points / diagram / screenshot works in the presentation, and I will tweak the deck while doing a dry-run when something doesn’t work.
And it’s often the case that the things speakers obsess about are the opposite of what the audience cares about. They want to be entertained. They want to learn. And most of all, they want you to do well.
That is key to remember, they want you to do well! Now, please take the time in the upcoming days to think about what you would like to talk about at a local VMUG. Everyone has something interesting to tell, it doesn’t need to be a deepdive on Storage, not everyone is Cormac Hogan right… No, a presentation on your migration between storage systems or datacenters could be just as interesting! A presentation on the introduction of a Disaster Recovery tool and how it changed your life would be a good way to help people making the right decision. Many many things one can talk about without the need to go extremely deep.
Once again, think about what you would like to talk about, create a slidedeck, practice and more importantly go have fun and support your local VMUG!!