Why do VSS snapshots cause Availability Groups to fail over?

Back in 2018, Ken Kellman and Erik Darling wrote that by freezing I/O on databases, VSS snapshots can cause Availability Groups to fail over. https://www.brentozar.com/archive/2018/01/perils-vss-snaps/

According to Erik, "the redo threads go buck wild on the other end."

OK. I've got buck wild redo threads. What does that mean?

I'm seeing one of my Availability Groups fail over on nearly a daily basis. This usually happens right around the time our Avamar server backups run. Is there anything that can, or should, be done to tame these buck wild redo threads of mine, and prevent this daily failover?


The failover policies are configurable - so you can adjust the thresholds


of course to do this you need to know which policy triggers the failover in the first place



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