Yellow Bricks

by Duncan Epping

vsan

Can I replicate, or snapshot, my vSAN Stretched Cluster Witness appliance for fast recovery?

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I’ve been seeing this question pop up more frequently, can I replicate or snapshot my vSAN Stretched Cluster Witness appliance for fast recovery? Usually, people ask this question as they cannot adhere to the 3-site requirement for a vSAN Stretched Cluster. So by setting up some kind of replication mechanism with low RPO, they try to mitigate this risk.

I guess the question stems from a lack of understanding of what the witness does. The witness provides a quorum mechanism, the quorum mechanism helps determine which site has access to the data in the case of a network failure (ISL) between the data locations.

Can I replicate, or snapshot, my vSAN Stretched Cluster Witness appliance for fast recovery?

So why can the Witness Appliance not be snapshotted or replicated then? Well, in order to provide this quorum mechanism, the Witness Appliance stores a witness component for each object. This is not per site, or per VM, but for every object… So if you have a VM with multiple VMDKs, you will have multiple witness objects per VM stored on the witness appliance. That witness object holds metadata and, through a log sequence number, understands which object holds the most recent data. This is where the issue arises. If you revert a Witness Appliance to an earlier point in time, the witness components also revert to an earlier point in time, and will have a different log sequence number than expected. This results in vSAN being unable to make the object available to the surviving site, or the site that is expected to hold quorum.

So in short, should you replicate or snapshot the Witness Appliance? No!

 

vSAN to vSAN Replication and Recovery Plan creation demo!

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As I was going through the various recordings I had of demos I created for Explore, I realized I hadn’t published the demos I created for vSAN to vSAN Replication, and on creating a Recovery Plan based on a vSAN Protection Group in VMware Live Recovery. So here it is. It is a pretty lengthy video as I go through all the various steps involved. So what you will see in this demo is the following:

  • vCenter Server Pairing between my 2 sites
  • Cluster pairing
  • Creation of a vSAN Protection Group, including vSAN to vSAN Replication
  • Creation of a Recovery Plan based on the previously created Protection Group
  • Test of the Recovery Plan

What happens after a Site Takeover when my failed sites come back online again?

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I got a question after the previous demo: what would happen if, after a Site Takeover, the two failed sites came back online again? I completely ignored this part of the scenario so far, I am not even sure why. I knew what would happen, but I wanted to test it anyway to confirm that what engineering had described actually happened. For those who cannot be bothered to watch a demo, what happens when the two failed sites come back online again is pretty straightforward. The “old” components of the impacted VMs are discarded, vSAN will recreate the RAID configuration as specified within the associated vSAN Storage Policy, and then a full resync will occur so that the VM is compliant again with the policy. Let me repeat one part: a full resync will occur! So if you do a Site Takeover, I hope you do understand what the impact will be. A full resync will take time, of course, depending on the connection between the data locations.

Does a Site Takeover work with a 2-node configuration?

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I got a question last week if vSAN Site Takeover also works with a 2-node configuration, and my answer was: yes, it should work. However, I had never tested it, so I figured I would build a quick lab environment and see if I was right. I recorded the result, here it is! The demo is pretty straight forward, let me describe what you will see:

  • 2-node vSAN environment
  • 1 VM named “photon-001”
  • Photon-001 VM is “stretched” across both hosts and has a witness component on the witness host
  • Host “.245” and the witness will fail and the components on those hosts will go “absent”
  • Photon-001 VM becomes inaccessible
  • We run the site-takeover command, which will reconfigure the Photon-001 VM
  • The Photon-001 VM becomes available again and it automatically restarted

#108 – My Explore recap: VCF Native S3 Object Storage, Cyber Recovery, and vSAN on FC!

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I had some difficulties scheduling guests the past weeks due to my travel schedule, and as a result, I figured I would try something new. In this episode, I go over the various things I announced at Explore and Explore on Tour in London, Paris, and Frankfurt. I talk about VCF Native S3 Object Storage, the enhancements we are planning for Disaster Recovery as well as Cyber Recovery, and I also briefly touch on vSAN on FC.

You can listen to my solo episode, episode 108, on Spotify (bit.ly/3MxRyZC), Apple Podcasts (bit.ly/4iEM5ML), or via the embedded player on Yellow-Bricks below.

If you like to hear more about vSAN ESA Global Deduplication, make sure ⁠to go to this blog on Yellow-Bricks⁠, as it contains the links to the discussion Pete Koehler and I had on the show a while back. I also just published the demo I recorded for Explore on Youtube, make sure to watch that one!

I also had Jatin Jindal on the show a month or two ago to discuss all Ransomware/Cyber Recovery enhancements in-depth. You can listen to that episode via Spotify (bit.ly/3IWQCwz), Apple (bit.ly/4o6YVoG), or via the embedded player on yellow-bricks.com!