docs(enable-xfs-quota) - documentation for applying xfs quota (#91)

* added enable-xfs.md

* changed name

* added loopback device  documentation

Author: almas33

docs/tutorials/hostpath/xfs_quota/create-xfs-fs-as-loopback-device.md

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+# Create XFS filesystem at the basepath as loopback device (if filesystem is not XFS)
+
+Create a 32Mb disk file which will be formatted as xfs filesystem, mounted as loopback device and exposed as the directory `/var/openebs/local`
+
+1. make sure library for managing xfs-fs is installed
+```console
+sudo apt update
+sudo apt-get install -y xfsprogs
+```
+
+2. make directory where mount will occur :-
+```console
+sudo mkdir -p /var/openebs/local
+cd /var/openebs
+```
+
+3. create sparse file of max size 32Mb using seek of max size 32Mb
+```console
+sudo dd if=/dev/zero of=xfs.32M bs=1 count=0 seek=32M
+```
+
+4. format the sparse file in xfs format
+```console
+sudo mkfs -t xfs -q xfs.32M
+```
+
+5. mount it as loopback device with project quota enabled
+```console
+sudo mount -o loop,rw xfs.32M -o pquota /var/openebs/local
+```

docs/tutorials/hostpath/xfs_quota/enable-xfs-quota.md

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+# OpenEBS LocalPV Hostpath Enable XFS Quota
+
+### Prerequisites
+
+1. A Kubernetes cluster with Kubernetes v1.16 or above is required
+2. All the nodes must have xfs utils installed
+3. The base path used by the provisioner should have XFS filesystem
+4. The base path used by the provisioner should be mounted with XFS project quotas enabled
+
+### Check Basepath
+Verify that filesystem is xfs
+```console
+stat -f -c %T /var/openebs/local
+```
+Filesystem of Basepath will be shown 
+```console
+xfs
+```
+
+Verify that project quotas are enabled
+```console
+xfs_quota -x -c state | grep 'Project quota state on /var/openebs/local' -A 2
+```
+Both Accounting and Enforcement should be ON
+```console
+Project quota state on /var/openebs/local (/dev/loop16)
+  Accounting: ON
+  Enforcement: ON
+```
+
+If project quotas are not enabled :-
+
+To set project quota on `/var/openebs/local`, enable project quota on `/var` filesystem,
+edit the `/etc/fstab` file, add `prjquota` after `default` keyword for `/var` file system
+```console
+$ vi /etc/fstab
+……………………………….
+/dev/mapper/Vol-var     /var     xfs     defaults,prjquota        0 0
+…………………………………
+```
+Then reboot the system
+
+
+### Installing
+Install the OpenEBS Dynamic LocalPV Provisioner using the following command:
+```console
+kubectl apply -f https://openebs.github.io/charts/openebs-operator-lite.yaml
+```
+Verify that pods in openebs namespace are running
+```console
+$ kubectl get pods -n openebs
+
+NAME                                           READY   STATUS    RESTARTS       AGE
+openebs-localpv-provisioner-6ddbd95d4d-htp7g   1/1     Running       0          7m12s
+openebs-ndm-operator-849d89cb87-djct8          1/1     Running       0          7m12s
+openebs-ndm-zd8lt                              1/1     Running       0          7m12s
+```
+
+### Deployment
+
+#### 1. Create a Storage Class
+```yaml
+apiVersion: storage.k8s.io/v1
+kind: StorageClass
+metadata:
+  name: openebs-hostpath-xfs
+  annotations:
+    openebs.io/cas-type: local
+    cas.openebs.io/config: |
+      - name: StorageType
+        value: "hostpath"
+      - name: BasePath
+        value: "/var/openebs/local/"
+provisioner: openebs.io/local
+volumeBindingMode: WaitForFirstConsumer
+reclaimPolicy: Delete
+parameters:
+  enableXfsQuota: 'true'
+  softLimitGrace: 20%
+  hardLimitGrace: 40%
+```
+`softLimitGrace` and `hardLimitGrace` with PV Storage Request will decide the soft limit and hard limit to be set.
+The size of a limit will be => size of PV Storage request * ( 1 + LimitGrace% )
+Anyone of hard limit or soft limit can also be used
+[Click here](https://man7.org/linux/man-pages/man8/xfs_quota.8.html#QUOTA_OVERVIEW) for detailed instructions about soft and hard limits.
+
+#### 2. Create a PVC with storage class
+```yaml
+kind: PersistentVolumeClaim
+apiVersion: v1
+metadata:
+  name: local-hostpath-pvc
+spec:
+  storageClassName: openebs-hostpath-xfs
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 5G
+```
+The PVC will be in 'Pending' state until the volume is mounted.
+```console
+$ kubectl get pvc
+
+NAME                  STATUS    VOLUME   CAPACITY   ACCESS MODES   STORAGECLASS          AGE
+local-hostpath-pvc   Pending                                      openebs-hostpath-xfs   21s
+```
+
+#### 3. Mount the Volume
+Mount the volume to the application pod container. The PVC status will change to 'Bound' when the volume is mounted to a container and quota is applied. A sample BusyBox Pod template is given below.
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+  name: busybox
+spec:
+  volumes:
+  - name: local-storage
+    persistentVolumeClaim:
+      claimName: local-hostpath-pvc
+  containers:
+  - name: busybox
+    image: busybox
+    command:
+       - sh
+       - -c
+       - 'while true; do echo "`date` [`hostname`] Hello from OpenEBS Local PV." >> /mnt/store/greet.txt; sleep $(($RANDOM % 5 + 300)); done'
+    volumeMounts:
+    - mountPath: /mnt/store
+      name: local-storage
+```
+Verify that quota is applied successfully
+```console
+master@node$ sudo xfs_quota -x -c 'report -h' /var/openebs/local/  
+Project quota on /var/openebs/local (/dev/loop16)
+                        Blocks              
+Project ID   Used   Soft   Hard Warn/Grace   
+---------- --------------------------------- 
+#0              0      0      0  00 [------]
+#1              0   5.7G   6.7G  00 [------]
+```
+#### Limitation
+* Resize of quota is not supported