In episode 30 we spoke with Alan Renouf about the potential future of edge deployments, aka Project Keswick. We figured we also need to cover what is available today in the form of VMware Edge Compute Stack, so we invited Marilyn Basanta who is the Senior Director at VMware for Edge! Marilyn explains what the VMware Edge Compute Stack looks like, what customer use cases she encounters in the field, and how VMware Edge Compute Stack can help you run and deploy applications securely and efficiently in remote, and sometimes strange, locations. You can listen via Spotify – spoti.fi/3WWNIKu , Apple – , or use the embedded player below! apple.co/3hEFu9L
Not sure why, but the last couple of weeks I have had several questions about FT (Fault Tolerance). The questions where around the limits, what is the limit per VM, what is the limit per host, and can I somehow exceed these? All of this is documented by VMware, but somehow seems to be either difficult to find or difficult to understand. Let me write a short summary that hopefully clarifies things.
First of all, the license you use dictates the maximum number of vCPUs a VM can have when enabling FT on that VM:
- vSphere Standard and Enterprise. Allows up to 2 vCPUs
- vSphere Enterprise Plus. Allows up to 8 vCPUs
Now, there are also two other things that come into play. You can have a maximum of 4 FT enabled VMs per host, and a maximum of 8 FT enabled vCPUs per host. You can change these settings, this is fully supported as I already discussed in this blog post. There is however a caveat, while VMware has tested with a higher number of FT enabled VMs per host than 4, and with a high number of FT enabled vCPUs, there’s no guarantee that you will get acceptable performance. The more you increase these default values, the bigger the chance that there will be a performance impact.
When FT is enabled a significant amount of communication between hosts (Primary / Shadow VM) needs to occur to ensure the VMs are in lockstep. This overhead can cause a slowdown, and this is the reason why we have those limitations in place. If you have sufficient networking bandwidth and CPU capacity then you can increase these numbers. However, if performance is impacted and you contact support then support may request to lower the numbers as that impact can unfortunately not be solved in a different way. I hope that clarifies it.
Starting with vSAN 8.0 ESA (Express Storage Architecture) VMware has introduced an adaptive RAID-5 mechanism. What does this mean? Essentially, vSAN deploys a particular RAID-5 configuration depending on the size of the cluster! There are two options, let’s list them out and discuss them individually.
- RAID-5, 2+1, 3-5 hosts
- RAID-5, 4+1, 6 hosts or more
As mentioned in the above list, depending on the cluster size, you will see a particular RAID-5 configuration. Clusters of up to 5 hosts will see a 2+1 configuration when RAID-5 is selected. For those wondering, the below diagram will show what this looks like. 2+1 configurations will have a 150% overhead, meaning that when you store 100GB of data, this will consume 150GB of capacity.
Now, when you have a larger cluster, meaning 6 hosts or more, vSAN will deploy a 4+1 configuration. The big benefit of this is that the “capacity overhead” goes down from 150% to 125%, in other words, 100GB of data will consume 125GB of capacity.
What is great about this solution is that vSAN will monitor the cluster size. If you have 6 hosts and a host fails, or a host is placed into maintenance mode etc, vSAN will automatically scale down the RAID-5 configuration from 4+1 to 2+1 after a time period of 24 hours. I of course had to make sure that it actually works, so I created a quick demo that shows vSAN changing the RAID-5 configuration from 4+1 to 2+1, and then back again to 4+1 when we reintroduce a host into the cluster.
One more thing I need to point out. The Adaptive RAID-5 functionality also works in a stretched cluster. So if you have a 3+3+1 stretched cluster you will see a 2+1 RAID-5 set. If you have a 6+6+1 cluster (or more in each location) then you will see a 4+1 set. Also, if you place a few hosts into maintenance mode or hosts have failed then you will see the configuration change from 4+1 to 2+1, and the other way around when hosts return for duty!
For more details, watch the demo, or read this excellent post by Pete Koehler on the VMware website.
Short answer, yes 2-node configurations with vSAN 8.0 ESA support Nested Fault Domains. Meaning that when you have a 2-node configuration you can also protect your data within each host with RAID-1, RAID-5, or RAID-6! The configuration of this is pretty straightforward. You create a policy with “Host Mirroring” and select the protection you want in each host. The screenshot below demonstrates this.
In the above example, I mirror the data across hosts and then have a RAID-5 configuration within each host. Now when I create a RAID-5 configuration within each host I will get the new vSAN ESA 2+1 configuration. (2 data blocks, 1 parity block) If you have 6 devices or more in your host, you can also create a RAID-6 configuration, which is 4+2. (4 data blocks, 2 parity blocks) This provides a lot of flexibility and can lower the overhead when desired. (RAID-1 = 100% overhead, RAID-5 = 50% overhead, RAID-6 = 25% overhead) When you use RAID-5 and RAID-6 and look at the layout of the data it will look as shown in the next two screenshots, the first screenshot shows the RAID-5 configuration, and the second the RAID-6 configuration.
One thing you may wonder when looking at the screenshots is why they also have a RAID-1 configuration for the VMDK object, this is the “performance leg” that vSAN ESA implements. For RAID-5, which is “FTT=1”, this means you get 2 components. For RAID-6, which is FTT=2, this means you will get 3 components so you can tolerate 2 failures.
I hope that helps answer some of the questions folks had on this subject!
At VMware Explore I was very intrigued by the sessions on vSphere Distributed Services Engine. After the session I briefly was in touch with Parag Chakraborty, Senior Product Line Manager for vSphere Distributed Services Engine (Project Monterey), and asked him if he wanted to join our podcast. Parag was enthusiastic and that is noticeable in this recording if you ask me. In this episode, he explains what is introduced in vSphere 8.0 by VMware with the vSphere Distributed Services Engine, why VMware is building a solution for SmartNICs/DPUs, what the benefits and use cases are, and goes over some operational considerations when adopting this new technology. It does make me wonder what datacenter infrastructure will look like in 10 years! Listen now via Spotify (spoti.fi/3S5NH3o), Apple (apple.co/3TqeRTr), or below via the embedded player.