docs/Cluster-VictoriaMetrics.md: clarify per-node workload increase when one of vmstorage node is unavailable in the cluster

The docs update is based on https://github.com/VictoriaMetrics/VictoriaMetrics/pull/6099#issuecomment-2060856417
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Aliaksandr Valialkin 2024-04-17 11:56:11 +02:00
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@ -466,8 +466,9 @@ General recommendations for cluster scalability:
since every `vmstorage` node contains lower number of time series when the number of `vmstorage` nodes increases.
The cluster stability is also improved with the number of `vmstorage` nodes, since active `vmstorage` nodes need to handle lower additional workload
when some of `vmstorage` nodes become unavailable. For example, if one node out of 5 is unavailable, 20% of the load is re-distributed across 4 remaining nodes.
If one node out of 10 nodes is unavailable, 10% of the load is re-distributed across 9 remaining node.
when some of `vmstorage` nodes become unavailable. For example, if one node out of 3 nodes is unavailable, then `1/3=33%` of the load is re-distributed across 2 remaining nodes,
so per-node workload increase is `(1/3/2)/(1/3) = 1/2 = 50%`.
If one node out of 10 nodes is unavailable, then `1/10=10%` of the load is re-distributed across 9 remaining nodes, so per-node workload increase is `(1/10/9)/(1/10) = 1/9 =~ 11%`.
- Adding more CPU and RAM to existing `vmstorage` nodes (aka vertical scaling) increases the number
of [active time series](https://docs.victoriametrics.com/FAQ.html#what-is-an-active-time-series) the cluster can handle.