Yellow Bricks

by Duncan Epping

VMware Cloud Foundation

New book: VMware vSAN 8.0 U1 Express Storage Architecture Deep Dive!

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We already gave some hints on twitter, and during an episode of the Unexplored Territory podcast, but here it finally is… The new book, the VMware vSAN 8.0 U1 Express Storage Architecture Deep Dive! It has been a year since we released the vSAN 7.0 U3 Deep Dive book, and with this brand new vSAN architecture being introduced in vSAN 8.0 we figured it was time to do a full overhaul of the book as well. Mind you, this new book purely deals with the Express Storage Architecture, aka vSAN ESA. This also means that some of the features which are not supported by ESA are not discussed in this book, for that you will need to buy the vSAN 7.0 U3 Deep Dive book, which covers OSA. Another big change is that we brought in a third author, we asked our good friend Pete Koehler to contribute to the book. Pete had done reviews of previous books, and considering the amount of material he produced for VMware Tech Marketing for vSAN (and ESA specifically) it made a lot of sense to bring him in!

VMware’s vSAN has rapidly proven itself in environments ranging from hospitals to oil rigs to e-commerce platforms and is the market leader in the hyperconverged space. Along the way, the world of IT has rapidly changed, not just from a software point of view, but also from a hardware perspective. With vSAN 8.0 VMware brought a new architecture to market called vSAN Express Storage Architecture (ESA). This architecture is highly optimized for today’s world of datacenter resources, be it CPU, memory, networking, or NVMe based flash storage.

The authors of the vSAN Deep Dive have thoroughly updated their definitive guide to this transformative technology. Writing for vSphere administrators, architects, and consultants, Cormac Hogan, Duncan Epping , and Pete Koehler explain what vSAN ESA is, why the architecture has changed, what it now offers, and how to gain maximum value from it. The book offers expert insight into preparation, installation, configuration, policies, provisioning, clusters, architecture, and more. You’ll also find practical guidance for using all data services, stretched clusters, two-node configurations, and cloud-native storage services.

Although we pressed publish on Tuesday, sometimes it takes a while before the book is available in all Amazon stores, but it should just trickle down in the upcoming 24-48 hours. The book is priced at 9.99 USD for the ebook and 29.99 USD for a paper copy, and is sold through Amazon only. Get it while it is hot, and we would appreciate it if you would use our referral links and leave a review when you finish it. Thanks for the support, and we hope you will enjoy it!

Of course, we also have the links to other major Amazon stores:

Changing the vSAN Skyline Health Interval

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On the VMTN forum Lars asked a great question, how do you change the vSAN Skyline Health interval. This used to be an option in the UI pre vSphere 7.0 but now seems to have disappeared. I never really touched it, so I had completely forgotten it was even an option at first. As vSAN also has an extensive CLI through “RVC”, and I used RVC before to disable a particular health check I figured this may also be a configurable setting, and indeed it is. It is rather straightforward:

SSH to your vCenter Server instance and open RVC. I use the following command to open an RVC session:

rvc administrator@vsphere.local@localhost

I then “cd” into my vSAN cluster object. Simply do an “ls” after you “cd” into a directory. My complete tree looks like this:

/localhost/Datacenter/computers/Cluster

When you are at the cluster level simply check the current configured interval:

vsan.health.health_check_interval_status .

Next you can configure the new internal, default setting is 60 minutes, but you can change it anywhere between 15 minutes and 1 day, I am configuring it to 15 minnutes:

vsan.health.health_check_interval_configure -i 15 .

Does vSAN Enhanced Durability work when you have a limited number of hosts?

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Last week I had a question about how vSAN Enhanced Durability works when you have a limited number of hosts. In this case, the customer had a 3+3+1 stretched cluster configuration, and they wondered what would happen when they would place a host into maintenance mode. Although I was pretty sure I knew what would happen, I figured I would test it in the lab anyway. Let’s start with a high-level diagram of what the environment looks like. Note I use a single VM as an example, just to keep the scenario easy to follow.

In the diagram, we see a virtual disk that is configured to be stretched across locations, and protected by RAID-1 within each location. As a result, you will have two RAID-1 trees each with two components and a witness, and of course, you would have a witness component in the witness location. Now the question is, what happens when you place esxi-host-1 into maintenance mode? In this scenario, vSAN Enhanced Durability will want to create a “durability component”. This durability component is used to commit all new write IO to. This will allow vSAN to resync fast after maintenance mode, and enhances durability as we would still have 2 copies of the (new) data.

However, in the scenario above we only have 3 hosts per location. The question then is, where is this delta component created then? As normally with maintenance mode you would need a 4th host to move data to. Well, it is simple, in this case, what vSAN does is it creates a “durability component” on the host where the witness resides, within the location of course. Let me show you in a diagram, as that makes it clear instantly.

By adding the Durability component next to the witness on esxi-host-3, vSAN enhances durability even in this stretched cluster situation, as it provides a local additional copy of new writes. Now, of course I tested this in my lab. So for those who prefer to see a demo, check out the youtube video below.

vSAN File Services and Stretched Clusters!

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As most of you probably know, vSAN File Services is not supported on a stretched cluster with vSAN 7.0 or 7.0U1. However, starting with vSAN 7.0 U2 we now fully support the use of vSAN File Services on a stretched cluster configuration! Why is that?

In 7.0 U2, you now have the ability to specify during configuration of vSAN File Services to which site certain IP addresses belong. In other words, you can specify the “site affinity” of your File Service services. This is shown in the screenshot below. Now I do want to note, this is a soft affinity rule. Meaning that if hosts, or VMs, fail on which these file services containers are running it could be that the container is restarted in the opposite location. Again, a soft rule, not a hard rule!

Of course, that is not the end of the story. You also need to be able to specify for each share with which location they have affinity. Again, you can do this during configuration (or edit it afterward if desired), and this basically then sets the affinity for the file share to a location. Or said differently, it will ensure that when you connect to file share, one of the file servers in the specified site will be used. Again, this is a soft rule, meaning that if none of the file servers are available on that site, you will still be able to use vSAN File Services,  just not with the optimized data path you defined.

Hopefully, that gives a quick overview of how you can use vSAN File Services in combination with a vSAN Stretched Cluster.  I created a video to demonstrate these new capabilities, you can watch it below.

vSAN 7.0 U2 now integrates with vSphere DRS

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One of the features our team requested a while back was integration between DRS and vSAN. The key use case we had was for stretched clusters. Especially in scenarios where a failure has occurred, it would be useful if DRS would understand what vSAN is doing. What do I mean by that?

Today when customers create a stretched cluster they have two locations. Using vSAN terminology these locations are referred to as the Preferred Fault Domain and the Secondary Fault Domain. Typically when VMs are then deployed, customers will create VM-to-Host Affinity Rules which state that VMs should reside in a particular location. When these rules are created DRS will do its best to ensure that the defined rule is adhered to. What is the problem?

Well if you are running a stretched cluster and let’s say one of the sites go down, then what happens when the failed location returns for duty is the following:

  • vSAN detects the missing components are available again
  • vSAN will start the resynchronization of the components
  • DRS runs every minute and rebalances and will move VMs based on the DRS rules

This means that the VMs for which rules are defined will move back to their respective location, even though vSAN is potentially still resynchronizing the data. First of all, the migration will interfere with the replication traffic. Secondly, for as long as the resync has not completed, I/O will across the network between the two locations, this will not only interfere with resync traffic, it will also increase latency for those workloads. So, how does vSAN 7.0 U2 solve this?

Starting with vSAN 7.0 U2 and vSphere 7.0 U2 we now have DRS and vSAN communicating. DRS will verify with vSAN what the state is of the environment, and it will not migrate the VMs back as long the VMs are healthy again. When the VMs are healthy and the resync has completed, you will see the rules being applied and the VMs automatically migrate back (when DRS is configured to Fully Automated that is).

I can’t really show it with a screenshot or anything, as this is a change in the vSAN/DRS architecture, but to make sure it worked I recorded a quick demo which I published through Youtube. Make sure to watch the video!