Longhorn can be used in Kubernetes to provide persistent storage through either Longhorn Container Storage Interface (CSI) driver or Longhorn FlexVolume driver. Longhorn will automatically deploy one of the drivers, depending on the Kubernetes cluster configuration. User can also specify the driver in the deployment yaml file. CSI is preferred.
Noted that the volume created and used through one driver won't be recongized by Kubernetes using the other driver. So please don't switch driver (e.g. during upgrade) if you have existing volumes created using the old driver. If you really want to switch driver, see [here](upgrade.md#migrating-between-flexvolume-and-csi-driver) for instructions.
2. Make sure `curl`, `findmnt`, `grep`, `awk` and `blkid` has been installed in the every node of the Kubernetes cluster.
#### Flexvolume driver directory
Longhorn now has ability to auto detect the location of Flexvolume directory.
If the Flexvolume driver wasn't installed correctly, there can be a few reasons:
1. If `kubelet` is running inside a container rather than running on the host OS, the host bind-mount path for the Flexvolume driver directory (`--volume-plugin-dir`) must be the same as the path used by the kubelet process.
1.1. For example, if the kubelet is using `/var/lib/kubelet/volumeplugins` as
the Flexvolume driver directory, then the host bind-mount must exist for that
directory, as e.g. `/var/lib/kubelet/volumeplugins:/var/lib/kubelet/volumeplugins` or any idential bind-mount for the parent directory.
1.2. It's because Longhorn would detect the directory used by the `kubelet` command line to decide where to install the driver on the host.
2. The kubelet setting for the Flexvolume driver directory must be the same across all the nodes.
2.1. Longhorn doesn't support heterogeneous setup at the moment.
### Environment check script
We've wrote a script to help user to gather enough information about the factors
