Docker interaction with Portworx

Docker interaction with Portworx

Portworx implements the Docker Volume Plugin Specification.

The plugin API allows creation, instantiation, and lifecycle management of Portworx volumes. This allows direct use by Docker, Docker swarm, and DCOS via dvdi.


Docker scans the plugin directory (/run/docker/plugins) on startup and whenever a user or a container requests a plugin by name. When the Portworx container is run, a unix domain socket pxd.sock is exported under /var/run/docker/plugins directory. Portworx volumes are shown as owned by volume driver pxd.



Portworx volumes are created by specifying volume driver as pxd.

Here is an example of how to create a 10GB volume with replication factor set to 3:

docker volume create --driver pxd \
           --opt size=10G \
           --opt repl = 3 \
           --name my_portworx_vol

Docker looks in its cache before sending the request to create to Portworx. For this reason, Portworx, Inc. recommends to not mix-and-match create and delete operations with pxctl and docker. If a volume with the same name is created again, it is a No-op.

Use of options in docker volume create

You can include any desired volume options with the volume create command:

--opt io_priority=high

The following table lists what options you can include:

Name Description Example
fs Specifies a filesystem to be laid out: xfs|ext4 fs: “ext4”
repl Specifies the replication factor for the volume: 1|2|3 repl: “3”
sharedv4 Creates a globally shared namespace volume which can be used by multiple pods over NFS with POSIX compliant semantics sharedv4: “true”
sharedv4_svc_type Indicates the mechanism Kubernetes will use for locating your sharedv4 volume. If you use this flag and there’s a failover of the nodes running your sharedv4 volume, you no longer need to restart your pods. Possible values are: ClusterIP or LoadBalancer. sharedv4_svc_type: “ClusterIP”
sharedv4_failover_strategy Specifies how aggressively to fail over to a new server for a Sharedv4 or Sharedv4 Service volume (Valid Values: aggressive, normal) sharedv4_failover_strategy: “aggressive”
priority_io Specifies IO Priority: low|medium|high. The default is low priority_io: “high”
io_profile Overrides I/O algorithm that Portworx uses for a volume. For more information about IO profiles, see the IO profiles section of the documentation. io_profile: “db”
group Specifies the group a volume should belong too. Portworx restricts replication sets of volumes of the same group on different nodes. If the force group option ‘fg’ is set to true, the volume group rule is strictly enforced. By default, it’s not strictly enforced. group: “volgroup1”
fg Enforces volume group policy. If a volume belonging to a group cannot find nodes for its replication sets which don’t have other volumes of the same group, the volume creation will fail. fg: “true”
label Arbitrary key=value labels that can be applied on a volume label: “name=mypxvol”
nodes Specifies comma-separated Portworx Node IDs to use for replication sets of the volume nodes: “minion1,minion2”
ephemeral Creates the ephemeral volumes ephemeral: false
size Specifies a volume size in GB (default 1) size: “1073741824”
scale Auto-scales the volume to a maximum number. (Valid Range: [1 1024]) (default 1) scale: 1
block_size Specifies a block size in Bytes (default 4096) block_size: “4096”
queue_depth Specifies a block device queue depth. (Valid Range: [1 256]) (default 128) queue_depth: 128
snap_interval Specifies an interval in minutes at which periodic snapshots will be triggered. Set to 0 to disable snapshots
snap_schedule Specifies the name of the snapshot schedule policy created using the pxctl sched-policy command Refer to this page for examples
secret_key Specifies Secret Key to be used for encrypting volumes Refer to the Secrets Management page for examples.
zones Specify comma-separated zone names in which the volume replicas should be distributed
racks Specify comma-separated rack names in which the volume replicas should be distributed
async_io Enables asynchronous IO for backing up storage async_io: false
csi_mount_options Specifies the mounting options for a volume through CSI
sharedv4_mount_options Specifies a comma-separated list of Sharedv4 NFS client mount options provided as key=value pairs
proxy_endpoint Specifies the endpoint address of the external NFS share Portworx is proxying proxy_endpoint: “nfs://<nfs-share-endpoint>”
proxy_nfs_subpath Specifies the sub-path from the NFS share to which this proxy volume has access to
proxy_nfs_exportpath Exports path for NFS proxy volume proxy_nfs_exportpath: “/<mount-path>”
export_options Defines the export options. Currently, only NFS export options are supported for Sharedv4 volumes
mount_options Specifies the mounting options for a volume when it is attached and mounted
best_effort_location_provisioning Requested nodes, zones, racks are optional
direct_io Enables Direct IO on a volume direct_io: “true”
scan_policy_trigger Specifies the trigger point on which filesystem check is triggered. Valid Values: none, on_mount, on_next_mount
scan_policy_action Specifies a filesystem scan action to be taken when triggered. Valid Values: none, scan_only, scan_repair
force_unsupported_fs_type Forces a filesystem type that is not supported. The driver may still refuse to use the type force_unsupported_fs_type: false
match_src_vol_provision Provisions the restore volume on the same pools as the source volume (src volume must exist)
nodiscard Mounts the volume with nodiscard option. This is useful when the volume undergoes a large amount of block discards and later the application rewrites to these discarded block making the discard work done by Portworx useless. This option must be used along with auto_fstrim. nodiscard: false
auto_fstrim Enables auto_fstrim on a volume and requires the nodiscard option to be set. Refer to this page for more details. auto_fstrim: true
storagepolicy Creates a volume on the Portworx cluster that follows the specified set of specs/rules. Refer this page for more details.
backend Specifies which storage backend Portworx is going to provide direct access to. (Valid Values: pure_block, pure_file) backend: “pure_block”
pure_export_rules Specifies the export rules for exporting a Pure Flashblade volume pure_export_rules: “*(rw)”
io_throttle_rd_iops Specifies maximum Read IOPs a volume will be throttled to. Refer to this page for more details. io_throttle_rd_iops: “1024”
io_throttle_wr_iops Specifies maximum Write IOPs a volume will be throttled to. Refer to this page for more details. io_throttle_wr_iops: “1024”
io_throttle_rd_bw Specifies maximum Read bandwidth a volume will be throttled to. Refer to this page for more details. io_throttle_rd_bw: “10”
io_throttle_wr_bw Specifies maximum Write bandwidth a volume will be throttled to. Refer to this page for more details. io_throttle_wr_bw: “10”
aggregation_level Specifies the number of replication sets the volume can be aggregated from aggregation_level: “2”
sticky Creates sticky volumes that cannot be deleted until the flag is disabled sticky: “true”
journal Indicates if you want to use journal device for the volume’s data. This will use the journal device that you used when installing Portworx. This is useful to absorb frequent syncs from short bursty workloads. Default: false journal: “true”
secure Creates an encrypted volume. For details about how you can create encrypted volumes, see the Create encrypted PVCs page. secure: “true”
placement_strategy Flag to refer the name of the VolumePlacementStrategy. For example:

kind: StorageClass
 name: postgres-storage-class
 placement_strategy: “postgres-volume-affinity”

For details about how to create and use VolumePlacementStrategy, see this page.
placement_strategy: “postgres-volume-affinity”
Creates scheduled snapshots with Stork. For example:
 schedulePolicyName: daily
  portworx/snapshot-type: local
 schedulePolicyName: weekly
  portworx/snapshot-type: cloud

Note: This example references two schedules:
  • The default-schedule backs up volumes to the local Portworx cluster daily.
  • The weekly-schedule backs up volumes to cloud storage every week.
For details about how you can create scheduled snapshots with Stork, see the Scheduled snapshots page.


Specify replica nodes

Multiple nodes through docker volume create is supported from

Use the nodes option to specify the nodes you wish the replicas to reside on.

Some valid examples of this are:

  • nodes=“4c4b3f62-3d23-43fb-9fa0-3b95b3236efc;7adc01d2-7c96-4446-8d2d-8f5e1035ec1e”
  • nodes=“4c4b3f62-3d23-43fb-9fa0-3b95b3236efc”
  • nodes=‘4c4b3f62-3d23-43fb-9fa0-3b95b3236efc;7adc01d2-7c96-4446-8d2d-8f5e1035ec1e’
  • nodes=‘4c4b3f62-3d23-43fb-9fa0-3b95b3236efc’
  • nodes=4c4b3f62-3d23-43fb-9fa0-3b95b3236efc

It is important to note that the number of nodes should equal the repl option otherwise Portworx will pick a node for the remaining requested replica’s.


Scheduled snapshots

Scheduled snapshots are only available in Portworx 1.3 and higher.

Use the _snapschedule option to specify the snapshot schedule.

Following are the accepted formats:


snaps-to-keep is optional. Periodic, Daily, Weekly and Monthly keep last 5, 7, 5 and 12 snapshots by default respectively.

Some examples of snapshots schedules are:

  • snap_schedule=“periodic=60,10”
  • snap_schedule=“daily=12:00,4”
  • snap_schedule=“weekly=sunday@12:00,2”
  • snap_schedule=“monthly=15@12:00”
Note that scheduled snapshots do not occur if the volume you are trying to snapshot is not attached to a container.

On-demand snapshots

There is no explicit Snapshot operation via Docker plugin API. However, this can be achieved via the create operation. Specifying a parent operation will create a snapshot.

The following command creates the volume snap_of_my_portworx_vol by taking a snapshot of my_portworx_vol

docker volume create --driver pxd \
           --opt parent=my_portworx_vol  \
           --name snap_of_my_portworx_vol

The snapshot can then be used as a regular Portworx volume.


Mount operation mounts the Portworx volume in the propagated mount location. If the device is un-attached, Mount will implicitly perform an attach as well. Mounts are reference counted and are idempotent. The same volume can be mounted at multiple locations on the same node. The same device can be mounted at the same location multiple times.


The docker plugin API does not have an Attach call. The Attach call is called internally via Mount on the first mount call for the volume.

Portworx exports virtual block devices in the host namespace. This is done via the Portworx container running on the system and does not rely on an external protocol such as iSCSI or NBD. Portworx virtual block devices only exist in host kernel memory. Two interesting consequences of this architecture are: 1) volumes can be unmounted from dead/disconnected nodes 2) IOs on porworx can survive a Portworx restart.

Portworx volume can be attached to any participating node in the cluster, although it can be attached to only one node at any given point in time. The node where the Portworx volume is attached is deemed the transaction coordinator and all I/O access to the volume is arbitrated by that node.

Attach is idempotent - multiple attach calls of a volume on the same node will return success. Attach on a node will return a failure, if the device is attached on a different node.

The following command will instantiate a virtual block device in the host namespace and mount it under propagated mount location. The mounted volume is then bind mounted under /data in the busybox container.

docker run -it -v my_portworx_vol:/data busybox c

Running it again will create a second instance of busybox, another bind mount and the Portworx volume reference count will be at 2. Both containers need to exit for the Portworx volume to be unmounted (and detached).


Umount operation unmounts the Portworx volume from the propagated mount location. If this is the last surviving mount on a volume, then the volume is detached as well. Once successfully unmounted the volume can be mounted on any other node in the system.


The docker plugin API does not have an Detach call. The Detach call is called internally via Unmount on the last unmount call for the volume.

Detach operation involves unexporting the virtual block device from the host namespace. Similar to attach, this is again accomplished via the Portworx container and does not require any external protocol. Detach is idempotent, multiple calls to detach on the same device will return success. Detach is not allowed if the device is mounted on the system.


Remove will delete the underlying Portworx volume and all associated data. The operation will fail if the volume is mounted.

The following command will remove the volume my_portworx_vol:

docker volume rm my_portworx_vol


The Portworx volume driver identifies itself as a global driver. Portworx operations can be executed on any node in the cluster. Portworx volumes can be used and managed from any node in the cluster.

Last edited: Tuesday, May 9, 2023