Are snapshots taken during upgrade backward-compatible?

Elastic Stack Elasticsearch
1

I have an upgrade planned that will take several days. There is a daily snapshot scheduled in SLM.

According to the documentation, "You can’t restore a snapshot to an earlier version of Elasticsearch".
According to the documentation for upgrades, "new functionality is disabled or operates in a backward compatible mode until all nodes in the cluster are upgraded."

Does that include snapshots? That is, can snapshots created while some nodes are upgraded, and some aren't, be restored to a cluster in which all of the nodes have the version before the upgrade?

Thanks!

2

Mostly yes, but there are situations where ES might consider itself to be "upgraded" even if you don't, and snapshots taken in that state might not restore cleanly into an earlier version.

Basically once you've started the upgrade you have to go through with it to completion.