How to mount a ceph-csi provisioned block-volume? - kubernetes

Question

I have a PVC like below:
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: raw-block-pvc
spec:
accessModes:
- ReadWriteOnce
volumeMode: Block
resources:
requests:
storage: 1Gi
storageClassName: csi-rbd-sc
It is provisioned by ceph-csi plugin. As you can see, it will perform as a block device in a Pod. And the Pod definition is like this:
---
apiVersion: v1
kind: Pod
metadata:
name: pod-with-raw-block-volume
spec:
containers:
- name: fc-container
image: nginx
volumeDevices:
- name: data
devicePath: /dev/xvda
volumes:
- name: data
persistentVolumeClaim:
claimName: raw-block-pvc
I can find it at /dev/xvda.
But when I try to mount it on a dir by mount /dev/xvda /mnt, it failed and showed following:
mount: /mnt: cannot mount /dev/xvda read-only.
Could anyone tell me what is the reason?

Answer 1

When you claim volumeMode as block in pvc , that's a raw block device, /dev/xvda is block device same as your linux hard disk. You can't mount one raw block device, it's not formatted , no file system on it.
If you want to attache storage to directory, you cloud claim filesystem volumemode.
here is a sample, more detail you could visit https://docs.ceph.com/en/latest/rbd/rbd-kubernetes/
$ cat <<EOF > pvc.yaml
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: rbd-pvc
spec:
accessModes:
- ReadWriteOnce
volumeMode: Filesystem
resources:
requests:
storage: 1Gi
storageClassName: csi-rbd-sc
EOF
$ kubectl apply -f pvc.yaml
$ cat <<EOF > pod.yaml
---
apiVersion: v1
kind: Pod
metadata:
name: csi-rbd-demo-pod
spec:
containers:
- name: web-server
image: nginx
volumeMounts:
- name: mypvc
mountPath: /var/lib/www/html
volumes:
- name: mypvc
persistentVolumeClaim:
claimName: rbd-pvc
readOnly: false
EOF
$ kubectl apply -f pod.yaml