Persistent volumes
Persistent volumes are storage which persist during & after pod's lifetime.
Persistent volumes in Rahti are stored in a resilient storage such as CEPH. They are created by using a PersistentVolumeClaim. When a new claim is made, and a Pod mounts it, a new volume space will be created.
A change from Rahti Beta version
In production Rahti, a new persistent volume will remain in "⏳ Pending" until any Pod mounts it. This is a change from Rahti Beta where the volume was crested right away.
There is one storage class available in Rahti:
- standard-csi. This is a "Read Write Once" (RWO) storage class, meaning that only one pod can mount the volume (in read-write mode).
More storage classes are on the work.
Persistent storage is requested in the cluster using PersistentVolumeClaim objects:
pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: testing-pvc
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
The example above will request a 1 GiB persistent storage that can be mounted in read-write mode by a single pod.
Persistent storage can be requested also via the web console.
Warning
When a volume contains a high amount of files (>15 000), the time it takes to mount and be available can be higher than 5 minutes. The more files, the more time it takes to be available.
The persistent volume can be used in a pod by specifying spec.volumes
(defines the volumes to attach) and spec.containers.volumeMounts (defines where
to mount the attached volumes in the container's filesystem):
pvc-pod.yaml:
apiVersion: v1
kind: Pod
metadata:
name: mypod-vol
labels:
app: serveapp-vol
pool: servepod-vol
spec:
containers:
- name: serve-cont
image: "image-registry.openshift-image-registry.svc:5000/openshift/httpd"
volumeMounts:
- mountPath: /mountdata
name: smalldisk-vol # Refers to your volume below
volumes:
- name: smalldisk-vol
persistentVolumeClaim:
claimName: testing-pvc # Refers to your PersistentVolumeClaim (pvc.yaml)
Warning
When a Persistent Volume is deleted, the corresponding data is deleted permanently. It is highly recommended to make regular and versioned copies of the data to an independent storage system like Allas.