[0:2:0:0]    disk    SMC      SMC2208          3.24  /dev/sda

[11:0:0:0]   disk    DATERA   IBLOCK           4.0   /dev/sdb


[root@tlx243 datera~iscsi]# mount  ``` grep sdb

/dev/sdb on /var/lib/kubelet/pods/6b99bd2a-628e-11e6-8463-0cc47ab41442/volumes/datera~iscsi/pv-datera-0 type xfs (rw,relatime,attr2,inode64,noquota)
  ```



Containers running in the pod see this device mounted at /data as specified in the manifest:



 ```
[root@tlx241 /]# kubectl exec kube-pv-demo -c data-pv-demo -it bash

root@kube-pv-demo:/# mount  ``` grep data

/dev/sdb on /data type xfs (rw,relatime,attr2,inode64,noquota)
  ```



**Using Pet Sets**



Typically, pods are treated as stateless units, so if one of them is unhealthy or gets superseded, Kubernetes just disposes it. In contrast, a PetSet is a group of stateful pods that has a stronger notion of identity. The goal of a PetSet is to decouple this dependency by assigning identities to individual instances of an application that are not anchored to the underlying physical infrastructure.



A PetSet requires {0..n-1} Pets. Each Pet has a deterministic name, PetSetName-Ordinal, and a unique identity. Each Pet has at most one pod, and each PetSet has at most one Pet with a given identity. A PetSet ensures that a specified number of “pets” with unique identities are running at any given time. The identity of a Pet is comprised of:

- a stable hostname, available in DNS
- an ordinal index
- stable storage: linked to the ordinal & hostname

A typical PetSet definition using a PersistentVolume Claim looks like below:



 ```
# A headless service to create DNS records

apiVersion: v1

kind: Service

metadata:

  name: test-service

  labels:

    app: nginx

spec:

  ports:

  - port: 80

    name: web

  clusterIP: None

  selector:

    app: nginx

---

apiVersion: apps/v1alpha1

kind: PetSet

metadata:

  name: test-petset

spec:

  serviceName: "test-service"

  replicas: 2

  template:

    metadata:

      labels:

        app: nginx

      annotations:

        [pod.alpha.kubernetes.io/initialized:](http://pod.alpha.kubernetes.io/initialized:) "true"

    spec:

      terminationGracePeriodSeconds: 0

      containers:

      - name: nginx

        image: [gcr.io/google\_containers/nginx-slim:0.8](http://gcr.io/google_containers/nginx-slim:0.8)

        ports:

        - containerPort: 80

          name: web

        volumeMounts:

        - name: pv-claim

          mountPath: /data

  volumeClaimTemplates:

  - metadata:

      name: pv-claim

      annotations:

        [volume.alpha.kubernetes.io/storage-class:](http://volume.alpha.kubernetes.io/storage-class:) anything

    spec:

      accessModes: ["ReadWriteOnce"]

      resources:

        requests:

          storage: 100Gi
  ```



We have the following PersistentVolume Claims available:



 ```
[root@tlx241 /]# kubectl get pvc

NAME                     STATUS    VOLUME        CAPACITY   ACCESSMODES   AGE

pv-claim-test-petset-0   Bound     pv-datera-0   0                        41m

pv-claim-test-petset-1   Bound     pv-datera-1   0                        41m

pv-claim-test-petset-2   Bound     pv-datera-2   0                        5s

pv-claim-test-petset-3   Bound     pv-datera-3   0                        2s
  ```



When this PetSet is provisioned, two pods get instantiated: