The meaning of system drained

Question

I am trying to understand the meaning of system drained within the systems/server context.

I will try give you an example:

Servers/Systems must be paused and drained prior to the patch cycle beginning.

Answer 1

Here you go,
https://techcommunity.microsoft.com/t5/failover-clustering/draining-nodes-for-planned-maintenance-with-windows-server-2012/ba-p/371713

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