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ceph-csi/docs/rbd-nbd.md
Prasanna Kumar Kalever 7576bf400c doc: update rbd-nbd doc about log path details 
Document the changes needed for configuring custom logging path

Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>
2021-08-24 07:15:30 +00:00

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RBD NBD Mounter

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.

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).

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

  • Edit the daemonset templates to change the cephLogDir

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

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

    • For standard templates edit csi-rbdplugin.yaml to update hostPath for ceph-logdir, also edit psp csi-nodeplugin-psp.yaml 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, then just 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.