# Local volume

Using HwameiStor can run stateful applications very easily.

Here we use a MySQL application as an example.

!!! note

    The MySQL Yaml file below is from [Kubernetes official repo](https://github.com/kubernetes/website/blob/main/content/en/examples/application/mysql/mysql-statefulset.yaml)

## View `StorageClass`

HwameiStor's Helm charts will install a `StorageClass` named `hwameistor-storage-lvm-hdd` by default, which can create local volumes.

Run the following command to open the YAML file.

```sh
kubectl get sc hwameistor-storage-lvm-hdd -o yaml
```

Modify the following YAML file.

```yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: hwameistor-storage-lvm-hdd
parameters:
  convertible: "false"
  csi.storage.k8s.io/fstype:xfs
  poolClass: HDD
  poolType: REGULAR
  replicaNumber: "1"
  striped: "true"
  volumeKind: LVM
provisioner: lvm.hwameistor.io
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true
```

If this `storageClass` was not generated during installation, run the following yaml file to regenerate it:

```sh
kubectl apply -f examples/sc-local.yaml
```

## Create `StatefulSet`

After HwameiStor and `StorageClass` are ready, one command can create MySQL container and its data volume:

```sh
kubectl apply -f sts-mysql_local.yaml
```

Note that `volumeClaimTemplates` uses `storageClassName: hwameistor-storage-lvm-hdd`:

```yaml
spec:
  volumeClaimTemplates:
  - metadata:
      name: data
      labels:
        app: sts-mysql-local
        app.kubernetes.io/name: sts-mysql-local
    spec:
      storageClassName: hwameistor-storage-lvm-hdd
      accessModes: ["ReadWriteOnce"]
      resources:
        requests:
          storage: 1Gi
```

and `schedulerName: hwameistor-scheduler`:

```yaml
spec:
  template:
    spec:
      schedulerName: hwameistor-scheduler
```

## View MySQL container and `PVC/PV`

In this example, the MySQL container is scheduled to node `k8s-worker-3`.

```console
$ kubectl get po -l app=sts-mysql-local -o wide
NAME READY STATUS RESTARTS AGE IP NODE
sts-mysql-local-0 2/2 Running 0 3m08s 10.1.15.154 k8s-worker-3

$ kubectl get pvc -l app=sts-mysql-local
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGE CLASS AGE VOLUME MODES
data-sts-mysql-local-0 Bound pvc-accf1ddd-6f47-4275-b520-dc317c90f80b 1Gi RWO hwameistor-storage-lvm-hdd 3m Filesystem
```

## View the `LocalVolume` object

By viewing `LocalVolume(LV)` with the same name as `PV`, you can see that the local volume is created on the node `k8s-worker-3`:

```console
$ kubectl get lv pvc-accf1ddd-6f47-4275-b520-dc317c90f80b

NAME POOL REPLICAS CAPACITY ACCESSIBILITY STATE RESOURCE PUBLISHED AGE
pvc-accf1ddd-6f47-4275-b520-dc317c90f80b LocalStorage_PoolHDD 1 1073741824 Ready-1 k8s-worker-3 3m
```

## [Optional] Scale the MySQL application into a three-node cluster

HwameiStor supports the horizontal expansion of `StatefulSet`. `StatefulSet` container will mount an independent local volume:

```console
$ kubectl scale sts/sts-mysql-local --replicas=3

$ kubectl get po -l app=sts-mysql-local -o wide
NAME READY STATUS RESTARTS AGE IP NODE
sts-mysql-local-0 2/2 Running 0 4h38m 10.1.15.154 k8s-worker-3
sts-mysql-local-1 2/2 Running 0 19m 10.1.57.44 k8s-worker-2
sts-mysql-local-2 0/2 Init:0/2 0 14s 10.1.42.237 k8s-worker-1

$ kubectl get pvc -l app=sts-mysql-local -o wide
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGE CLASS AGE VOLUME MODES
data-sts-mysql-local-0 Bound pvc-accf1ddd-6f47-4275-b520-dc317c90f80b 1Gi RWO hwameistor-storage-lvm-hdd 3m07s Filesystem
data-sts-mysql-local-1 Bound pvc-a4f8b067-9c1d-450f-aff4-5807d61f5d88 1Gi RWO hwameistor-storage-lvm-hdd 2m18s Filesystem
data-sts-mysql-local-2 Bound pvc-47ee308d-77da-40ec-b06e-4f51499520c1 1Gi RWO hwameistor-storage-lvm-hdd 2m18s Filesystem

$ kubectl get lv
NAME POOL REPLICAS CAPACITY ACCESSIBILITY STATE RESOURCE PUBLISHED AGE
pvc-47ee308d-77da-40ec-b06e-4f51499520c1 LocalStorage_PoolHDD 1 1073741824 Ready-1 k8s-worker-1 2m50s
pvc-a4f8b067-9c1d-450f-aff4-5807d61f5d88 LocalStorage_PoolHDD 1 1073741824 Ready-1 k8s-worker-2 2m50s
pvc-accf1ddd-6f47-4275-b520-dc317c90f80b LocalStorage_PoolHDD 1 1073741824 Ready-1 k8s-worker-3 3m40s
```