Support partition parameter

[saad-ali]

GCE PD in-tree driver supports partitioning

    gcePersistentDisk:
      pdName: partitioned-disk
      fsType: ext4
      partition: 2

[ehmm]

Hi @saad-ali, @davidz627 I've created a quick patch that works that allows specifying the partition number as another parameters after the zone/volumeName. (https://github.com/ehmm/gcp-compute-persistent-disk-csi-driver/tree/feature/partitionInVolumeId)

As you can see I'm new here, so I don't know if you want to merge it, or maybe it's missing some testing (I see the unit-tests there) -- or just leave it for now, but leaving a link here in the mean time and if you want me to create a PR let me know.

[davidz627]

/assign

I will be adding partitioning to volume_attributes. This reduces the amount of string parsing we have to do. We also want the volumeID to be as stable as possible (affects backwards/forwards compatibility) and don't want to set a precedent of adding extra information to the volume ID when needed. Volume attributes is a natural place for this new functionality to exist.

[msau42]

Can you uniquely identify a volume if the volume id doesn't contain partition number though? ie multiple volumes on the same disk but on different partitions

[davidz627]

You're right, the volumes are uniquely identified via volume ID so we would have conflicts here. I will change the PR to include partitions in Volume ID.

[davidz627]

Additionally just found this in the spec:

Attributes MAY NOT uniquely identify
a volume. A volume uniquely identified by `id` SHALL always report
the same attributes.

just as extra reason to put it in the volume id

[msau42]

@ehmm For your usecase, do you need hard capacity isolation (ie partition boundaries) or could using subdirectories + Kubernetes subpath feature work for you?

I think representing each partition as a separate PV in Kubernetes has some challenges with Pod scheduling, attaching and detaching, that I pointed out in #91

[ehmm]

@msau42 for my use case the subPath solution would be great, I also wouldn't mind just having the root with all the subdirectories exposed as I have no isolation requirements. I personally don't imagine a lot of scenarios where isolation requirements would be needed, and I think that auto-mounting all partitions (with any supported fsType #93) is a good idea for general use cases.

[davidz627]

Currently partition cannot be specified in attributes, it runs into the same issue as described with the in tree GCE PD here: kubernetes/kubernetes#57915.

Since @ehmm is no longer depending on this feature we will punt this until a general solution for both In-tree and CSI versions of GCE PD can be made. That will require core Kubernetes changes and will be tracked at the following issue: kubernetes/kubernetes#57915.