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Resource Optimization

Kubernetes allows much easier and efficient resource utilization, in JuiceFS CSI Driver, there's much to be done in this aspect. Methods on resource optimizations are introduced in this chapter.

Adjust resources for mount pod​

Every application pod that uses JuiceFS PV requires a running mount pod (reused for pods using a same PV), thus configuring proper resource definition for mount pod can effectively optimize resource usage.

Read the official documentation Resource Management for Pods and Containers to learn about pod resource requests and limits. For a default JuiceFS mount pod, resource requests is 1 CPU and 1GiB memory, resource limits is 2 CPU and 5GiB memory.

Static provisioning​

Set resource requests and limits in PersistentVolume:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: juicefs-pv
  labels:
    juicefs-name: ten-pb-fs
spec:
  capacity:
    storage: 10Pi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  csi:
    driver: csi.juicefs.com
    volumeHandle: juicefs-pv
    fsType: juicefs
    nodePublishSecretRef:
      name: juicefs-secret
      namespace: default
    volumeAttributes:
      juicefs/mount-cpu-limit: 5000m
      juicefs/mount-memory-limit: 5Gi
      juicefs/mount-cpu-request: 100m
      juicefs/mount-memory-request: 500Mi

Dynamic provisioning​

Set resource requests and limits in StorageClass:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: juicefs-sc
provisioner: csi.juicefs.com
parameters:
  csi.storage.k8s.io/provisioner-secret-name: juicefs-secret
  csi.storage.k8s.io/provisioner-secret-namespace: default
  csi.storage.k8s.io/node-publish-secret-name: juicefs-secret
  csi.storage.k8s.io/node-publish-secret-namespace: default
  juicefs/mount-cpu-limit: 5000m
  juicefs/mount-memory-limit: 5Gi
  juicefs/mount-cpu-request: 100m
  juicefs/mount-memory-request: 500Mi

If StorageClass is managed by Helm, you can define mount pod resources directly in values.yaml:

values.yaml
storageClasses:
- name: juicefs-sc
  enabled: true
  ...
  mountPod:
    resources:
      requests:
        cpu: "100m"
        memory: "500Mi"
      limits:
        cpu: "5"
        memory: "5Gi"

Share mount pod for the same StorageClass​

By default, mount pod is only shared when multiple application pods are using a same PV. However, you can take a step further and share mount pod (in the same node, of course) for all PVs that are created using the same StorageClass, under this policy, different application pods will bind the host mount point on different paths, so that one mount pod is serving multiple application pods.

To enable mount pod sharing for the same StorageClass, add the STORAGE_CLASS_SHARE_MOUNT environment variable to the CSI Node Service:

kubectl -n kube-system set env -c juicefs-plugin daemonset/juicefs-csi-node STORAGE_CLASS_SHARE_MOUNT=true

Evidently, more aggressive sharing policy means lower isolation level, mount pod crashes will bring worse consequences, so if you do decide to use mount pod sharing, make sure to enable automatic mount point recovery as well, and increase mount pod resources.

Clean cache when mount pod exits​

Refer to relevant section in Cache.

Delayed mount pod deletion​

note

This feature requires JuiceFS CSI Driver 0.13.0 and above.

Mount pod will be re-used when multiple applications reference a same PV, JuiceFS CSI Node Service will manage mount pod life cycle using reference counting: when no application is using a JuiceFS PV anymore, JuiceFS CSI Node Service will delete the corresponding mount pod.

But with Kubernetes, containers are ephemeral and sometimes scheduling happens so frequently, you may prefer to keep the mount pod for a short while after PV deletion, so that newly created pods can continue using the same mount pod without the need to re-create, further saving cluster resources.

Delayed deletion is controlled by a piece of config that looks like juicefs/mount-delete-delay: 1m, this supports a variety of units: ns (nanoseconds), us (microseconds), ms (milliseconds), s (seconds), m (minutes), h (hours).

With delete delay set, when reference count becomes zero, the mount pod is marked with the juicefs-delete-at annotation (a timestamp), CSI Node Service will schedule deletion only after it reaches juicefs-delete-at. But in the mean time, if a newly created application needs to use this exact PV, the annotation juicefs-delete-at will be emptied, allowing new application pods to continue using this mount pod.

Config is set differently for static and dynamic provisioning.

Static provisioning​

In PV definition, modify the volumeAttributes field, add juicefs/mount-delete-delay:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: juicefs-pv
  labels:
    juicefs-name: ten-pb-fs
spec:
  capacity:
    storage: 10Pi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  csi:
    driver: csi.juicefs.com
    volumeHandle: juicefs-pv
    fsType: juicefs
    nodePublishSecretRef:
      name: juicefs-secret
      namespace: default
    volumeAttributes:
      juicefs/mount-delete-delay: 1m

Dynamic provisioning​

In StorageClass definition, modify the parameters field, add juicefs/mount-delete-delay:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: juicefs-sc
provisioner: csi.juicefs.com
parameters:
  csi.storage.k8s.io/provisioner-secret-name: juicefs-secret
  csi.storage.k8s.io/provisioner-secret-namespace: default
  csi.storage.k8s.io/node-publish-secret-name: juicefs-secret
  csi.storage.k8s.io/node-publish-secret-namespace: default
  juicefs/mount-delete-delay: 1m

PV Reclaim Policy​

Reclaim policy dictates what happens to data in storage after PVC or PV is deleted. Retain and Delete are the most commonly used policies, Retain means PV (alongside with its associated storage asset) is kept after PVC is deleted, while the Delete policy will remove PV and its data in JuiceFS when PVC is deleted.

Static provisioning​

Static provisioning only support the Retain reclaim policy:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: juicefs-pv
  labels:
    juicefs-name: ten-pb-fs
spec:
  capacity:
    storage: 10Pi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  csi:
    driver: csi.juicefs.com
    volumeHandle: juicefs-pv
    fsType: juicefs
    nodePublishSecretRef:
      name: juicefs-secret
      namespace: default

Dynamic provisioning​

For dynamic provisioning, reclaim policy is Delete by default, can be changed to Retain in StorageClass definition:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: juicefs-sc
provisioner: csi.juicefs.com
reclaimPolicy: Retain
parameters:
  csi.storage.k8s.io/provisioner-secret-name: juicefs-secret
  csi.storage.k8s.io/provisioner-secret-namespace: default
  csi.storage.k8s.io/node-publish-secret-name: juicefs-secret
  csi.storage.k8s.io/node-publish-secret-namespace: default

Running CSI Node Service on select nodes​

JuiceFS CSI Driver consists of CSI Controller, CSI Node Service and Mount Pod. Refer to JuiceFS CSI Driver Architecture for details.

By default, CSI Node Service (DaemonSet) will run on all nodes, users may want to run it only on nodes that really need to use JuiceFS, to further reduce resource usage.

Add node label​

Add label for nodes that actually need to use JuiceFS, for example, mark nodes that need to run model training:

# Adjust nodes and label accordingly
kubectl label node [node-1] [node-2] app=model-training

Modify JuiceFS CSI Driver installation configuration​

Install via Helm​

Add nodeSelector in values.yaml:

values.yaml
node:
  nodeSelector:
    app: model-training

Install JuiceFS CSI Driver:

helm install juicefs-csi-driver juicefs/juicefs-csi-driver -n kube-system -f ./values.yaml

Install via kubectl​

Either edit juicefs-csi-node.yaml and run kubectl apply -f juicefs-csi-node.yaml, or edit directly using kubectl -n kube-system edit daemonset juicefs-csi-node, add the nodeSelector part:

k8s.yaml
apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: juicefs-csi-node
  namespace: kube-system
  ...
spec:
  ...
  template:
    spec:
      nodeSelector:
        # adjust accordingly
        app: model-training
      containers:
      - name: juicefs-plugin
        ...
...

Uninstall CSI Controller​

The CSI Controller component exists for a single purpose: PV provisioning when using Dynamic Provisioning. So if you have no use for dynamic provisioning, you can safely uninstall CSI Controller, leaving only CSI Node Service:

kubectl -n kube-system delete sts juicefs-csi-controller

If you're using Helm:

values.yaml
controller:
  enabled: false

Considering that CSI Controller doesn't really take up a lot of resources, this practice isn't really recommended, and only kept here as a reference.

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