Container Storage Interface (CSI) support

[yasker]

CSI became beta in v1.10, we should start working on supporting it.

[errorsandwarnings]

@yasker

In CSI only file volumes are supported. I think longhorn is a block volume interface. Correct ?

Read Here

What are the limitations of alpha?
The alpha implementation of CSI has the following limitations:
The credential fields in CreateVolume, NodePublishVolume, and ControllerPublishVolume calls are not supported.
Block volumes are not supported; only file.
Specifying filesystems is not supported, and defaults to ext4.
CSI drivers must be deployed with the provided “external-attacher,” even if they don’t implement “ControllerPublishVolume”.
Kubernetes scheduler topology awareness is not supported for CSI volumes: in short, sharing information about where a volume is provisioned (zone, regions, etc.) to allow k8s scheduler to make smarter scheduling decisions.

[yasker]

A block storage can be easily presented as a file system by formatting it. But a file system cannot be present as a block storage.

[yasker]

Majority of the support is in with longhorn/longhorn-manager#68

Pending on #106

[yasker]

Done.