If you want separate volumes per each Pod in statefulSet: you need to use volumeClaimTemplate - is really a PVC, but templatized:
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: mysql
labels:
app: mysql
spec:
template:
metadata:
labels:
app: mysql
spec:
containers:
- name: mysql
image: mysql
volumeMounts:
- mountPath: /var/lib/mysql
name: data-volume
replicas:3
selector:
matchLabels:
app: mysql
serviceName: mysql-h
volumeClaimTemplates:
- metadata:
name: data-volume
spec:
accessModes:
- ReadWriteOnce
storageClassName: google-storage
resources:
requests:
storage: 300Mi