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Using Per-Volume FileSystem Options with Kubernetes

Introduction

The Pure Service Orchestrator Kubernetes CSI driver includes support for per-volume basis filesystem (FS) options starting with version 5.0.5. The feature allows Kubernetes end-users to create persistent volumes with customizable filesystem options on a per-volume basis. Users can customize the filesystem type (FsType) with create options (CreateOptions) during the volume staging phase and customize mount options (MountOptions) during the volume publish phase.

The feature leverages Kubernetes StorageClass to carry the customized FS options to the underlying storage backend. Before this feature, users could only set up these parameters via configuration in the values.yaml file. Then all persistent volumes used the same options, and the settings could not be changed after PSO had loaded. With this feature, users can customize the FS options for persistent volumes on-the-fly through various StorageClass settings to meet different application needs.

Dependencies

The following dependencies must be true before the customized filesystem options can be used:

  • Kubernetes already running, deployed, configured, etc
  • For the MountOptions feature, ensure you have Kubernetes 1.8+ installed.
  • PSO correctly installed and using Pure CSI Driver v5.0.5+.

FileSystem Options

PSO leverages Kubernetes StorageClass to pass the customized FS options to the underlying storage backend. If the FS options are specified in the StorageClass, it will override the default values from the values.yaml. The default values will only apply when no FS options in the StorageClass.

FsType

The CSI external-provisioner allows users to set FsType via key-value parameters map in the StorageClass. You can use the pre-defined key "csi.storage.k8s.io/fstype" to set up the FsType like this:

parameters:
    csi.storage.k8s.io/fstype: vfat

CreateOptions

PSO allows users to set CreateOptions via key-valume parameters map in the StorageClass. You can use the pre-defined key "createoptions" to set up the CreateOptions like this:

parameters:
    createoptions: -F 32 -f 2 -S 512 -s 1 -R 32

MountOptions

Persistent Volumes that are dynamically created by a StorageClass will have the MountOptions specified in the mountOptions field of the StorageClass. You can set the options like this:

mountOptions:
    - nosuid
    - discard

Notes:

  1. Native mkfs and mount support: Please make sure your worker nodes support the FsType with the correct CreateOptions you specify in the StorageClass.

    During the Volume staging phase, PSO transfer these parameters to our driver and creates the file system for a volume using the command like this mkfs.<FsType> -o <CreateOptions> /dev/dm-0. Failure of mkfs operation will lead pod volume attachment failures and pod will be stuck in pending state. It is also true when you mount with incorrect MountOptions. For FlashBlade, make sure your worker nodes have NFS utilities package installed:

 yum install -y nfs-utils

  1. FlashBlade support: When you backend storage type is FB, PSO will ignore the FsType and CreateOptions parameters by default since FB does not allow users to format the filesystem when you attach volumes. The default filesystem for FB is nfs. However, users can still specify the MountOptions to mount volumes.

  2. Kubenetes default Filesystem: Kubernetes uses ext4 as the default file systems. If users do not specify FsType in the StorageClass, K8s will pass the default ext4 to the driver. PSO recommends users to use xfs to achieve the best performance.

  3. Default "discard" mount option: By default, PSO automatically adds a "discard" option while mounting the volume to achieve the best performance unless users specifically add the "nodiscard" option, which PSO does not recommend.

Example of StorageClass for FlashArray

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: pure-block-xfs
  labels:
    kubernetes.io/cluster-service: "true"
provisioner: pure-csi 
parameters:
    backend: block
    csi.storage.k8s.io/fstype: xfs
    createoptions: -q
mountOptions:
      - discard

To apply:

kubectl apply -f https://raw.githubusercontent.com/purestorage/helm-charts/master/docs/examples/fsoptions/pure-block-xfs.yaml

Example of StorageClass for FlashBlade

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: pure-file-nfs
  labels:
    kubernetes.io/cluster-service: "true"
provisioner: pure-csi 
parameters:
    backend: file
mountOptions:
      - nfsvers=3
      - tcp

To apply:

kubectl apply -f https://raw.githubusercontent.com/purestorage/helm-charts/master/docs/examples/fsoptions/pure-file-nfs.yaml