docs(volume): add raw block volume docs with a usecase (#149)

Signed-off-by: prateekpandey14 <[email protected]>

docs/tutorial/intro.md

@@ -19,3 +19,4 @@ On a high level, this tutorial covers following:
 2. This [link](./volumes/snapshot.md) explains the volume snapshot related operations.
 3. This [link](./volumes/resize.md) explains the volume resize related operations.
 4. This [link](./volumes/migration.md) explains the volume migration related operations across k8s nodes.
+5. This [link](./volumes/block_volume.md) explains how to use cstor raw block volume.

docs/tutorial/volumes/block_volume.md

@@ -0,0 +1,115 @@
+# CStor CSI RAW Block Volume:
+
+When using a raw block volume in your Pods, you must specify a VolumeDevice attribute
+in the Container section of the PodSpec rather than a VolumeMount. VolumeDevices
+have devicePaths instead of mountPaths, and inside the container, applications 
+will see a device at that path instead of a mounted file system.
+
+A block volume will appear as a block device inside the container,and allows 
+low-level access to the storage without intermediate layers, as with file-system
+volumes.There are advantages of raw disk partitions for example:
+
+- Block devices that are actually SCSI disks support sending SCSI commands to the
+  device using Linux ioctls.
+- Faster I/O without UNIX file system overhead, and more synchronous I/O without
+  UNIX file system buffering etc.
+
+### How to use block volume
+
+There is a number of use cases where a raw block device will be useful. For example,
+A user can use a raw block device for database applications such as MySQL to read 
+data from and write the results to a disk that has a formatted filesystem to be 
+displayed via the nginx web server.
+
+The following sections describe some sample volume specifications and steps to dynamically 
+provision a raw block volume and attach it to an application pod.
+
+### Creating a new raw block PVC
+1. Raw Block volume:
+
+```yaml
+kind: PersistentVolumeClaim
+apiVersion: v1
+metadata:
+  name: block-claim
+spec:
+  volumeMode: Block
+  storageClassName: cstor-disk-stripe
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 5Gi
+
+```
+
+2. Filesystem based volume:
+
+```yaml
+kind: PersistentVolumeClaim
+apiVersion: v1
+metadata:
+  name: fs-claim
+spec:
+  storageClassName: cstor-disk-stripe
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 5Gi
+```
+
+
+### Using a raw Block PVC in POD
+
+Here, the user creates an application pod/deployment, having 2 containers consume both block &
+filesystem volumes. We have to choose devicePath for the block device inside the
+Mysql container rather than the mountPath for the file system. Nginx container
+we have mounted the filesystem based volume.
+
+```yaml
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  labels:
+    run: mysql
+  name: mysql
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      run: mysql
+  strategy: {}
+  template:
+    metadata:
+      labels:
+        run: mysql
+    spec:
+      containers:
+      - image: mysql
+        imagePullPolicy: IfNotPresent
+        name: mysql
+        volumeDevices:
+          - name: my-db-data
+            devicePath: /dev/block
+        env:
+          - name: MYSQL_ROOT_PASSWORD
+            value: test
+      - image: nginx
+        imagePullPolicy: IfNotPresent
+        name: nginx
+        ports:
+          - containerPort: 80
+        volumeMounts:
+          - name: my-nginx-data
+            mountPath: /usr/share/nginx/html
+            readOnly: false
+      volumes:
+        - name: my-db-data
+          persistentVolumeClaim:
+            claimName: block-claim
+        - name: my-nginx-data
+          persistentVolumeClaim:
+            claimName: fs-claim
+```
+