Managing Block Volume Access Modes

A block volume can be accessible in read/write or read-only mode depending on the following controls:

• ​The ​accessModes​​ parameter specified in the PVC definition. The parameter lists allowed PVC access modes for any pods mounting the volume. VAST Block CSI Driver supports the following modes:

  • For raw block volumes (​​volumeMode: block​​): ReadOnlyMany (ROX), ReadWriteOnce (RWO), ReadWriteOncePod (RWOP), ReadWriteMany (RWX)

    ​Note that the ReadWriteMany (RWX) mode for raw block devices can only be implemented with cluster-aware file systems.

  • ​For filesystem volumes (​​volumeMode: filesystem​​): ReadOnlyMany (ROX), ReadWriteOnce (RWO), ReadWriteOncePod (RWOP)

  NOTE: See ​here​​ for a detailed explanation of these access modes.

• The ​readOnly​ flag of a pod (set to true or false). This flag lets you restrict access by a particular pod to read-only, which may override the access mode specified by the PVC's ​accessModes​​ parameter.

  ​The ​readOnly​ flag can only be applied for filesystem volumes (​volumeMode: filesystem​​). If set for a raw block volume (​volumeMode: block​​), the driver ignores the flag.

To allow concurrent read access by multiple pods to a raw block volume:

• ​​Specify in the PVC:

  spec:
    accessModes:
      - ReadOnlyMany
    volumeMode: Block

• Ensure that none of the pods has the ​readOnly​​ flag set.

To allow read/write access to a raw or filesystem block volume by any one pod on the same node at a time:

• Specify in the PVC:

  spec:
    accessModes:
      - ReadWriteOnce
    volumeMode: {Block|Filesystem}

• Ensure that none of the pods has the ​readOnly​​ flag set.

To allow concurrent read/write access by multiple pods to the same raw block volume:

• Specify in the PVC:

  spec:
    accessModes:
      - ReadWriteMany
    volumeMode: Block

• Ensure that none of the pods has the ​readOnly​​ flag set.

To allow concurrent read/write access to a filesystem volume by multiple pods except one:

• Specify in the PVC:

  spec:
    accessModes:
      - ReadWriteOnce
    volumeMode: Filesystem

• Specify in the pod that is not allowed to write:

  spec:
    containers:
        volumeMounts:
          -  readOnly: true 

To allow read/write access to a raw or filesystem block volume by exactly one pod at a time (cluster-wide):

• Specify in the PVC:

  spec:
    accessModes:
      - ReadWriteOncePod
    volumeMode: {Block|Filesystem}