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November 11th, 2021 08:00
7.0.300 Stretched cluster site/witness failure resiliency
Hi guys, I just read the release notes of the 7.0.300 and this new feature is very interesting in my environment: 6 Vxrail nodes splitted on two building, witness temporary in one of the two building.
- Stretched cluster site/witness failure resiliency. This release enables stretched clusters to tolerate planned or unplanned downtime of a site and the witness. You can perform site-wide maintenance (such as power or networking) without concerns about witness availability.
This means that I don't need anymore to move the witness in a third site or to external cloud? How it works?
Thanks
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DELL-Naoyuki K
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November 11th, 2021 18:00
> This means that I don't need anymore to move the witness in a third site or to external cloud? How it works?
No. In my understanding, it's still the same requirement for witness site.
How it works, is described in external blog.
vSAN 7.0 U3 enhanced stretched cluster resiliency, what is it? | Yellow Bricks (yellow-bricks.com)
Let's say, DC A and witness are in the same site A', and DC B is in the site B', in this case, if the site A' becomes totally down, all the object in DC B also becomes down because of loss of quorum.
If witness is in third site, and there is enough time between loss of DC A and Witness site and then all the object could change the vote layout (make it vote 0 in witness site), all the object in DC B would still remain accessible.
Cipo80
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November 22nd, 2021 02:00
Hi Naoyuki,
thank you for the Duncan blog link.
I've understand, In simple word, by U3 if something go wrong and DC A and Witness go down for maximum 5 minutes (?) nothing happened:
Starting with 7.0 U3 this behavior has changed. If Datacenter A fails, and a few (let’s say 5) minutes later the witness disappears, all replicated objects would still be available! So why is this? Well in this scenario, if Datacenter A fails, vSAN will create a new votes layout for each of the objects impacted. It basically will assume that the witness can fail and give all components on the witness 0 votes, on top of that it will give the components in the active site additional votes so that we can survive that second failure. If the witness would fail, it would not render the objects inaccessible as quorum would not be lost.