Limitations

The known limitations of IBM Spectrum Scale Container Storage Interface driver are provided in this section.

  • IBM Spectrum Scale Container Storage Interface driver does not honor the size that is specified in PersistentVolumeClaim for lightweight volume. The df command inside a container does not show the correct volume size in the container for lightweight volumes. Instead, this command shows the size of the file system or fileset based on the filesetdf configuration.
  • The df command inside the container shows only one entry per file system even when multiple PVCs from IBM Spectrum Scale are attached to the container or pod. Use --all option of df command to list all the entries.
  • For IBM Spectrum Scale Container Storage Interface driver CSI 2.8.0 and prior releases, GUI service of all clusters configured on custom resource must always be running, in case if one or more GUI host becomes unavailable, this may result in CSI driver pod going into crashloopback state if CSI driver pod restarts for any reason.
  • Maximum number of supported volumes that can be created by using independent fileset storage class is 998, excluding the root fileset and primary fileset reserved for IBM Spectrum Scale Container Storage Interface driver. The maximum number of volumes that can be created are 2998 in IBM Spectrum Scale 5.1.4.0 or later. This limitation is based on the number of filesets that are supported by IBM Spectrum Scale. For more information, see IBM Spectrum® Scale FAQ in the IBM Spectrum Scale documentation.
    Note: fsType mentioned in the storageClass definition does not have any impact on the IBM Spectrum Scale Container Storage Interface driver. The fsType value (gpfs) is displayed in the PersistentVolume (PV) details.
  • Primary filesystem defined in custom resource is used by CSI for internal purpose. Primary filesystem has to be available all the time for CSI functionality. Changing primary filesystem after deployment is not recommended as this will result in old volume becoming unusable.
  • Primary fileset inside primary filesystem is used by CSI for internal functionality. It must be linked all the time at the same location and should not be used for hosting any other data.
  • Changing the mount of filesystems on k8s cluster is likely to result in previous volumes (if any) created from those filesystem becoming unusable.
  • IBM Spectrum Scale Container Storage Interface driver relies on the GUI server for doing IBM Spectrum Scale operations during volume provisioning or deprovisioning and attach or detach. If the GUI password or CA certificate expires, then manual intervention is needed by the administrator to reset the password on GUI or generate a new certificate and update the configuration in IBM Spectrum Scale Container Storage Interface driver.
  • IBM Spectrum Scale Container Storage Interface driver does not support ReadOnlyMany access mode of PVC.Start of change The ReadOnly access can be enabled by using the readOnly: true parameter of the pod specification.End of change
  • IBM Spectrum Scale file systems must remain mounted on the worker nodes while IBM Spectrum Scale Container Storage Interface driver is running. If unmounted for some reason, it might affect pods on a node mounting the volumes from these file systems, and you need to restart the node to mount the file system back.
  • Volume provisioning and attachment operations rely on REST API status. Occasionally, there will be some delay in reflecting the file system status from the cluster into the REST API. In such instances, you might experience interim failures in volume provisioning and attach or detach operations, which go away when the REST API status is updated.
  • Although multiple instances of the IBM Spectrum Scale GUI are allowed, the IBM Spectrum Scale Container Storage Interface driver is limited to point to a single GUI node.
  • IBM Spectrum Scale Container Storage Interface driver does not support the rolling upgrade of IBM Spectrum Scale while IBM Spectrum Scale Container Storage Interface driver or Operator pods are running on the worker nodes.
  • In dynamic provisioning or consistency group, if the PVC is deleted before it goes into bound state then the fileset that is created for that PVC might not get deleted. You need to delete the fileset manually.
  • In the static provisioning, the softlink must be resolved on the Kubernetes cluster for proper functioning. If the softlinks are not resolved, then you might have different file system mount points on the owning and the accessing cluster. This setup can lead to mounting or data access issue.
  • Start of changeWhile using fsGroup for large volumes, checking and changing the ownership and permissions can take longer that slowing down the Pod startup. You can use the fsGroupChangePolicy control in such a way that Kubernetes checks and manages the ownership and permissions for a volume.End of change
  • Start of changefsGroup support is applicable to previously created volume as well and is applied as soon as existing pod is restarted with IBM Spectrum Scale Container Storage Interface driver Driver 2.6 or later. If you do not desire to have this effect, remove fsGroup from pod's securityContext.End of change
  • GUI High Availability feature in the CSI driver should be used only with IBM Spectrum Scale 5.1.6.1 and above.
  • The following limitations are specific to the Volume Snapshots and Volume Cloning features:
    • Hard links from the source snapshot are copied as regular files during volume creation from the snapshot.
    • Performance of the volume creation from the snapshot operation depends on the level of subdirectories that exist in the snapshot and the data resides within the subdirectories. As the number of nested sub directories increases, the volume creation operation gets slower.
    • While creating PVC from the snapshot, the minimum size of the new PVC must be at least 1 GB as the initial fileset-based PVC, whose snapshot is used as a datasource, results in 1 GB PV.
    • You must have the default snapshots directory as .snapshots for filesets in IBM Spectrum Scale to use the snapshot feature for a consistency group.
    • Specifying different CA signed certificates for GUI host is not supported while configuring the GUI High Availability feature in the IBM Spectrum Scale CSI driver custom resource.