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Are Nested Fault Domains supported with 2-node configurations with vSAN 8.0 ESA?

Duncan Epping · Oct 28, 2022 · 5 Comments

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.

vSAN ESA 2-node nested fault domain raid-5

vSAN ESA 2-node nested fault domain raid-6

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!

 

Related

Storage, vSAN esa, express storage architecture, VMware, vsan 8, vsan 8.0, vsan esa

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Comments

  1. Roger Uebelhart says

    28 October, 2022 at 11:00

    Great article, Duncan.

    Does here also apply the adaptive RAID5 config? Let‘s assume I have 3 disks in my vSAN nodes with RAID5 (2+1) and I‘m going to add 3 more disks. Will vSAN adapt within 24h to a 4+1 here as well?

    Kind regards
    Roger

    Reply
    • Duncan Epping says

      28 October, 2022 at 11:34

      I have not experienced this in my lab. I have asked the engineering team what the expected behavior is, but I doubt that is how it works. Even in a 6 device configuration I see a 2+1 RAID-5 configuration.

      Reply
    • Duncan Epping says

      11 November, 2022 at 09:41

      Validated it with the engineering team. RAID-5 is always 2+1 in this 2-NODE Nested Configuration. So you have 3 options:
      RAID-5 – 2+1 (150% overhead)
      RAID-1 – Mirroring (200% overhead)
      RAID-6 – 4+2 (125% overhead)

      Reply
  2. Nicolas Bohn Jacobsen says

    28 October, 2022 at 14:24

    With 2-node configuration don´t you have witness ?
    Also in the above screenshots shouldn´t it be on different hosts (IP addresses)

    Reply
    • Duncan Epping says

      28 October, 2022 at 20:12

      Yes you have a witness on the witness node and you have a similar RAID tree on the other host as well. I am only showing 1 host as otherwise it would be more difficult to grasp. But you are right.

      Reply

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About the author

Duncan Epping is a Chief Technologist in the Office of CTO of the Cloud Platform BU at VMware. He is a VCDX (# 007), the author of the "vSAN Deep Dive", the “vSphere Clustering Technical Deep Dive” series, and the host of the "Unexplored Territory" podcast.

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