ceph-csi/docs/rbd-nbd.md

RBD NBD Mounter

• RBD NBD Mounter
  • Overview
  • Configuration
    • Configuring logging path
  • Status
  • Support Matrix
    • CSI spec and Kubernetes version compatibility

Overview

The RBD CSI plugin will provision new RBD images and attach and mount those to workloads. Currently, the default mounter is krbd, which uses the kernel rbd driver to mount the rbd images onto the application node. Here on at ceph-csi we will also have a userspace way of mounting the RBD images, via RBD-NBD.

Rbd-nbd is a client for RADOS block device (rbd) images like the existing rbd kernel module. It will map an rbd image to an NBD (Network Block Device) device, allowing access to it as a regular local block device.

It’s worth to make a note that the rbd-nbd processes will run on the client-side, which is inside the csi-rbdplugin node plugin.

Configuration

To use the rbd-nbd mounter for RBD-backed PVs, set mounter to rbd-nbd in the StorageClass.

Please note that the minimum recommended kernel version to use rbd-nbd is 5.4 or higher.

Configuring logging path

If you are using the default rbd nodePlugin DaemonSet and StorageClass templates then cephLogDir will be /var/log/ceph, this directory will be a host-path and the default log file path will be /var/log/ceph/rbd-nbd-<volID>.log. rbd-nbd creates a log file per volume under the cephLogDir path on NodeStage(map) and removed the same on the respective NodeUnstage(unmap).

• There are different strategies to maintain the logs

  • remove: delete log file on unmap/detach (default behaviour)
  • compress: compress the log file to gzip on unmap/detach, in case there exists a .gz file from previous map/unmap of the same volume, then override the previous log with new log.
  • preserve: preserve the log file in text format

  You can tweak the log strategies through cephLogStrategy option from the storageclass yaml

• In case if you need a customized log path, you should do below:

  • Edit the DaemonSet templates to change the ceph log directory host-path

    • If you are using helm charts, then you can use key cephLogDirHostPath

      helm install --set cephLogDirHostPath=/var/log/ceph-csi/my-dir
      

    • For standard templates edit csi-rbdplugin.yaml to update hostPath for ceph-logdir. to update pathPrefix spec entries.

  • Update the StorageClass with the customized log directory path

    • Now update rbd StorageClass for cephLogDir, for example

      cephLogDir: "/var/log/prod-A-logs"
      

NOTE:

• On uninstall make sure to delete cephLogDir on host manually to freeup some space just in case if there are any uncleaned log files.
• In case if you do not need the rbd-nbd logging to persistent at all, then simply update the StorageClass for cephLogDir to use a non-persistent path.

Status

Rbd-nbd support status: Alpha

Support Matrix

Features	Feature Status	CSI Driver Version	Ceph Cluster Version	CSI Spec Version	Kubernetes Version
Creating and deleting snapshot	Alpha	>= v3.4.0	Pacific (>=16.0.0)	>= v1.0.0	>= v1.17.0
Creating and deleting clones	Alpha	>= v3.4.0	Pacific (>=16.0.0)	>= v1.0.0	>= v1.17.0
Creating and deleting encrypted volumes	Alpha	>= v3.4.0	Pacific (>=16.0.0)	>= v1.0.0	>= v1.14.0
Expand volumes	Alpha	>= v3.4.0	Pacific (>=16.0.0)	>= v1.1.0	>= v1.15.0

NOTE: The Alpha status reflects possible non-backward compatible changes in the future, and is thus not recommended for production use.

CSI spec and Kubernetes version compatibility

Please refer to the matrix in the Kubernetes documentation.