Summary
I’m running a homelab Kubernetes cluster with multiple nodes. One node hosts a ZFS pool. I’m provisioning volumes over iSCSI via this Helm chart. I want different block sizes per StorageClass: PostgreSQL at 8K (to match its page size) and everything else (backup-like data) at the default 16K.
However, PVCs created from both StorageClasses end up with volblocksize=16K.

What I expected

• StorageClass A (postgres): volblocksize=8K
• StorageClass B (default/backup): volblocksize=16K

What actually happened

• Both volumes are created with volblocksize=16K.

Repro (abridged)

Abridged values.yaml:

csiDriver:
  name: "org.democratic-csi.iscsi"

storageClasses:
  - name: ssd-iscsi
    defaultClass: false
    reclaimPolicy: Delete
    volumeBindingMode: Immediate
    allowVolumeExpansion: true
    parameters:
      fsType: xfs
      volblocksize: 16K
  - name: ssd-iscsi-2
    defaultClass: false
    reclaimPolicy: Delete
    volumeBindingMode: Immediate
    allowVolumeExpansion: true
    parameters:
      fsType: xfs
      volblocksize: 8K

driver:
  config:
    driver: zfs-generic-iscsi
    sshConnection:
      host: n2p1
      username: democratic-csi
      privateKey: |
        -----BEGIN OPENSSH PRIVATE KEY-----
        ...
        -----END OPENSSH PRIVATE KEY-----

    zfs:
      cli:
        sudoEnabled: true

      datasetProperties:
        "volblocksize": "{{ parameters.volblocksize }}"

      datasetParentName: nas/k8s
      detachedSnapshotsDatasetParentName: tanks/k8s/test-snapshots

      zvolEnableReservation: false

# sudo zfs get volblocksize nas/k8s/pvc-c44942d4-0142-498c-aa93-051ac59afb34 nas/k8s/pvc-f000b4ba-2414-4cfe-8c43-fb2b6be8ad43
NAME                                              PROPERTY      VALUE     SOURCE
nas/k8s/pvc-c44942d4-0142-498c-aa93-051ac59afb34  volblocksize  16K       default
nas/k8s/pvc-f000b4ba-2414-4cfe-8c43-fb2b6be8ad43  volblocksize  16K       default

What I found in the code
While tracing the provisioning path, I noticed that the value from datasetProperties.volblocksize is being overwritten later in the flow (

Questions

1. Is there a specific reason volblocksize from datasetProperties is always overwritten?
2. If not, can we change the precedence so that datasetProperties (per StorageClass) has the highest priority?

Rationale

• PostgreSQL benefits from 8K blocks to align with its page size and reduce write amplification.
• Backup/archival data can stay on 16K to optimize throughput/fragmentation differently.
• Being able to tune this per StorageClass is a common operational need.