According to official K8S documentation:

The access modes are:

ReadWriteOnce – the volume can be mounted as read-write by a single node

ReadOnlyMany – the volume can be mounted read-only by many nodes

ReadWriteMany – the volume can be mounted as read-write by many nodes

I've created one Persistent Volume with RWO access mode. I've applied PVC:

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: readwriteonce-test
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 8Gi
  storageClassName: ""

and Deployment:

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: test-deployment
spec:
  selector:
    matchLabels:
      app: test-deployment
  replicas: 3
  template:
    metadata:
      labels:
        app: test-deployment
    spec:
      containers:
      - name: test-pod
        image: "gcr.io/google_containers/busybox:1.24"
        command:
          - "/bin/sh"
        args:
          - "-c"
          - "rm -R /data/*; while :; do ls /data/; name=$(date '+%s'); echo \"some data in file ${name}\" >> \"/data/${name}.txt\" ; sleep 10; cat \"/data/${name}.txt\"; done"
        imagePullPolicy: IfNotPresent
        volumeMounts:
        - mountPath: /data
          name: test-volume
      restartPolicy: Always
      volumes:
      - name: test-volume
        persistentVolumeClaim:
          claimName: readwriteonce-test

PeristentVolume:

Name:            readwriteonce-test
Labels:          volume-name=readwriteonce-test
Annotations:     kubectl.kubernetes.io/last-applied-configuration:
                   {"apiVersion":"v1","kind":"PersistentVolume","metadata":{"annotations":{},"labels":{"volume-name":"readwriteonce-test"},"name":"readwriteo...
Finalizers:      [kubernetes.io/pv-protection]
StorageClass:    
Status:          Bound
Claim:           ***/readwriteonce-test
Reclaim Policy:  Retain
Access Modes:    RWO
VolumeMode:      Filesystem
Capacity:        8Gi
Node Affinity:   <none>
Message:         
Source:
    Type:      NFS (an NFS mount that lasts the lifetime of a pod)
    Server:    ***.efs.eu-west-1.amazonaws.com
    Path:      /readwriteonce-test
    ReadOnly:  false
Events:        <none>

The Question is:

Could anyone explain me, why there is no error in such configuration? As you can see, each pod have been mounted on different nodes. Each pod is able to see files created by other pods.

screenshot