Create harvester.md

Author: patrick-hermann-sva

harvester.md

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+# HARVESTER
+
+<details>
+  <summary>ReplicaSchedulingFailure Single-Node Harvester Cluster</summary>
+  
+You have a single-node Harvester cluster (sthings)
+Longhorn is configured for 3 replicas per volume
+Only 1 replica can run because Longhorn's anti-affinity prevents multiple replicas on the same node
+Status: ReplicaSchedulingFailure: precheck new replica failed
+
+Why this happens:
+Longhorn's default configuration assumes multi-node clusters for data redundancy. With one node, it can't satisfy the "3 replicas on different nodes" requirement.
+Solutions:
+
+```bash
+For existing volumes
+kubectl --kubeconfig ~/.kube/harvester patch volume pvc-2ae20462-92b3-4ce2-93f5-8d90812b03bb \
+  -n longhorn-system --type=merge -p '{"spec":{"numberOfReplicas":1}}'
+
+kubectl --kubeconfig ~/.kube/harvester patch volume pvc-5626539c-5b15-4b9c-8bf9-cda3625887a4 \
+  -n longhorn-system --type=merge -p '{"spec":{"numberOfReplicas":1}}'
+
+# Set global default for future volumes
+kubectl --kubeconfig ~/.kube/harvester patch settings.longhorn.io default-replica-count \
+  -n longhorn-system --type=merge -p '{"value":"1"}'
+```
+</details>
+
+
+