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title: Block Storage
weight: 22
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---
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# Block Storage

Block storage allows you to mount storage to a single pod. This example shows how to build a simple, multi-tier web application on Kubernetes using persistent volumes enabled by Rook.

## Prerequisites

This guide assumes you have created a Rook cluster as explained in the main [Quickstart](ceph-quickstart.md) guide.

## Provision Storage

Before Rook can start provisioning storage, a StorageClass and its storage pool need to be created. This is needed for Kubernetes to interoperate with Rook for provisioning persistent volumes. For more options on pools, see the documentation on [creating storage pools](ceph-pool-crd.md).

Save this storage class definition as `storageclass.yaml`:

```yaml
apiVersion: ceph.rook.io/v1beta1
kind: Pool
metadata:
  name: replicapool
  namespace: rook-ceph
spec:
  replicated:
    size: 3
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
   name: rook-ceph-block
provisioner: ceph.rook.io/block
parameters:
  pool: replicapool
  # The value of "clusterNamespace" MUST be the same as the one in which your rook cluster exist
  clusterNamespace: rook-ceph
  # Specify the filesystem type of the volume. If not specified, it will use `ext4`.
  fstype: xfs
```

Create the storage class.
```bash
kubectl create -f storageclass.yaml
```

## Consume the storage: Wordpress sample

We create a sample app to consume the block storage provisioned by Rook with the classic wordpress and mysql apps.
Both of these apps will make use of block volumes provisioned by Rook.

Start mysql and wordpress from the `cluster/examples/kubernetes` folder:

```bash
kubectl create -f mysql.yaml
kubectl create -f wordpress.yaml
```

Both of these apps create a block volume and mount it to their respective pod. You can see the Kubernetes volume claims by running the following:

```bash
$ kubectl get pvc
NAME             STATUS    VOLUME                                     CAPACITY   ACCESSMODES   AGE
mysql-pv-claim   Bound     pvc-95402dbc-efc0-11e6-bc9a-0cc47a3459ee   20Gi       RWO           1m
wp-pv-claim      Bound     pvc-39e43169-efc1-11e6-bc9a-0cc47a3459ee   20Gi       RWO           1m
```

Once the wordpress and mysql pods are in the `Running` state, get the cluster IP of the wordpress app and enter it in your browser:

```bash
$ kubectl get svc wordpress
NAME        CLUSTER-IP   EXTERNAL-IP   PORT(S)        AGE
wordpress   10.3.0.155   <pending>     80:30841/TCP   2m
```

You should see the wordpress app running.

If you are using Minikube, the Wordpress URL can be retrieved with this one-line command:

```console
echo http://$(minikube ip):$(kubectl get service wordpress -o jsonpath='{.spec.ports[0].nodePort}')
```

**NOTE:** When running in a vagrant environment, there will be no external IP address to reach wordpress with.  You will only be able to reach wordpress via the `CLUSTER-IP` from inside the Kubernetes cluster.

## Consume the storage: Toolbox

With the pool that was created above, we can also create a block image and mount it directly in a pod. See the [Direct Block Tools](direct-tools.md#block-storage-tools) topic for more details.

## Teardown

To clean up all the artifacts created by the block demo:

```
kubectl delete -f wordpress.yaml
kubectl delete -f mysql.yaml
kubectl delete -n rook-ceph pool replicapool
kubectl delete storageclass rook-ceph-block
```

## Advanced Example: Erasure Coded Block Storage

If you want to use erasure coded pool with RBD, your OSDs must use `bluestore` as their `storeType`.
Additionally the nodes that are going to mount the erasure coded RBD block storage must have Linux kernel >= `4.11`.

To be able to use an erasure coded pool you need to create two pools (as seen below in the definitions): one erasure coded and one replicated.
The replicated pool must be specified as the `pool` parameter. It is used for the metadata of the RBD images.
The erasure coded pool must be set as the `dataPool` parameter below. It is used for the data of the RBD images.

```yaml
apiVersion: ceph.rook.io/v1beta1
kind: Pool
metadata:
  name: replicated-metadata-pool
  namespace: rook-ceph
spec:
  replicated:
    size: 3
---
apiVersion: ceph.rook.io/v1beta1
kind: Pool
metadata:
  name: ec-data-pool
  namespace: rook-ceph
spec:
  # Make sure you have enough nodes and OSDs running bluestore to support the replica size or erasure code chunks.
  # For the below settings, you need at least 3 OSDs on different nodes (because the `failureDomain` is `host` by default).
  erasureCoded:
    dataChunks: 2
    codingChunks: 1
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
   name: rook-ceph-block
provisioner: ceph.rook.io/block
parameters:
  pool: replicated-metadata-pool
  dataPool: ec-data-pool
  # Specify the namespace of the rook cluster from which to create volumes.
  # If not specified, it will use `rook` as the default namespace of the cluster.
  # This is also the namespace where the cluster will be
  clusterNamespace: rook-ceph
  # Specify the filesystem type of the volume. If not specified, it will use `ext4`.
  fstype: xfs
```

(These definitions can also be found in the [`ec-storageclass.yaml`](https://github.com/rook/rook/blob/{{ branchName }}/cluster/examples/kubernetes/ceph/cluster.yaml) file)