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Version: 3.1

Create and manage volumes using pxctl

This topic explains how to create and manage volumes using the pxctl CLI tool. To view a list of the pxctl commands, run one of the following from a worker node:

export PATH=$PATH:/opt/pwx/bin
pxctl volume --help
/opt/pwx/bin/pxctl volume --help

Alternatively, you can run the following commands anywhere you can access your Kubernetes cluster. First, set an environment variable containing the name of one of your Portworx worker nodes:

PX_POD=$(kubectl get pods -l name=portworx -n <px-namespace> -o jsonpath='{.items[0].metadata.name}')

Then you can run pxctl commands through kubectl exec as follows:

kubectl exec $PX_POD -n <px-namespace> -- /opt/pwx/bin/pxctl volume --help

The following sections explain the individual pxctl commands.

Create volumes​

Portworx creates volumes from the global capacity of a cluster. You can expand the capacity and throughput of your cluster by adding new nodes to the cluster. Portworx protects your volumes from hardware and node failures through automatic replication.

Consider the following capabilities of Portworx when creating a new volume using the pxctl CLI:

  • Durability: Set the replication level through policy, using the High Availability setting. For more information, see storage policy.
  • Portworx synchronously replicates each write operation to a quorum set of nodes.
  • Portworx uses an elastic architecture. This allows you to add capacity and throughput at every layer, at any time.
  • Volumes are thinly provisioned. They only use as much storage as needed by the container.
  • You can expand and contract the maximum size of a volume, even after you write data to the volume.

To create a volume, run the pxctl volume create command and provide the volume name. The following example creates the myVol volume:

pxctl volume create myVol
3903386035533561360
note

Portworx controls the throughput at per-container level and can be shared. Volumes have fine-grained control, set through policy.

Before proceeding to the next sections, understand the following concepts:

  • Throughput is set by the IO Priority setting. Throughput capacity is pooled.
  • If you add a node to the cluster, you expand the available throughput for read and write operations.
  • Portworx selects the best node to service read operations, no matter that the operation is from local storage devices or the storage devices attached to another node.
  • Read throughput is aggregated, where multiple nodes can service one read request in parallel streams.
  • Fine-grained controls: Policies are specified per volume and provide full control to storage.
  • Policies enforce how the volume replicates across the cluster, IOPs priority, filesystem, blocksize, and additional parameters described below.
  • Policies are specified at create time, and you can apply them to the existing volumes.

The pxctl CLI tool provides options for setting the policies on a volume. Run the pxctl volume create command with the --help flag to view the available options.

note

You can also pass these options through the scheduler.

Create volumes with a specific filesystem formatting​

You can use the pxctl volume create command with the --fs option to specify your desired filesystem (ext4 or xfs) and --fs_format_options to specify your desired filesystem formatting options for the specified filesystem.

Use it only for volumes that are formatted with either ext4 or exfs filesystems.

Here are a few examples for specifying different filesystems and filesystem formatting options for a volume:

  • EXT4: pxctl volume create vol3 --fs ext4 --fs_format_options "-i 8192". To see all the formatting options for ext4, see the mkfs man page.
  • EXT4: pxctl volume create vol2 --fs ext4 --fs_format_options "-N 128000". To see all the formatting options for ext4, see the mkfs.ext4 man page.
  • XFS: pxctl volume create vol9 --fs xfs --fs_format_options "-q -i size=1024". To see all the formatting options for ext4, see the [mkfs.xfs man page](: https://linux.die.net/man/8/mkfs.xfs).

Alternatively, run man mkfs.ext4 or man mkfs.xfs on linux terminal to see the man page details.

Place a replica on a specific node​

Use the --nodes=LocalNode flag to create a volume and place at least one replica of the volume on the node where the command is run. This is useful when you use a script to create a volume locally on a node.

note

You can provide a node ID, node IP address, or pool UUID to the --nodes flag.

For example, run the following command to create the localVolume volume and place a replica of the volume on the local node:

pxctl volume create --nodes=LocalNode localVolume
Volume successfully created: 756818650657204847

The following command helps you to check if the replica of the volume is on the node where the command was run:

pxctl volume inspect localVolume
Volume  :  756818650657204847
        Name                     :  localVolume
        Size                     :  1.0 GiB
        Format                   :  ext4
        HA                       :  1
        IO Priority              :  LOW
        Creation time            :  Mar 20 00:30:05 UTC 2019
        Shared                   :  no
        Status                   :  up
        State                    :  detached
        Reads                    :  0
        Reads MS                 :  0
        Bytes Read               :  0
        Writes                   :  0
        Writes MS                :  0
        Bytes Written            :  0
        IOs in progress          :  0
        Bytes used               :  340 KiB
        Replica sets on nodes:
                Set 0
                  Node           : X.X.X.90 (Pool 1)
        Replication Status       :  Detached
note

The replicas are visible in the Replica sets on nodes section of the command output.

pxctl volume list --name opt_example
ID			NAME		SIZE	HA	SHARED	ENCRYPTED	IO_PRIORITY	STATUS		SNAP-ENABLED
282820401509248281	opt_example	1 GiB	1	no	no		LOW		up - detached	no

The pxctl CLI utility supports the following key-value pairs:

IO priority      - io_priority=[high|medium|low]
Volume size      - size=[1..9][G|M|T]
HA factor        - repl=[1,2,3]
Block size       - bs=[4096...]
Shared volume    - shared=true
File System      - fs=[xfs|ext4]
Encryption       - passphrase=secret
snap_schedule    - "periodic=mins#k;daily=hh:mm#k;weekly=weekday@hh:mm#k;monthly=day@hh:mm#k" where k is the number of snapshots to retain.

The global namespace​

Through sharedv4 volumes (also known as a global namespace), a single volume’s filesystem is concurrently available to multiple containers running on multiple hosts.

note
  • You do not need to use sharedv4 volumes to have your data accessible on any host in the cluster. Any Portworx volumes can be exclusively accessed from any host as long as they are not simultaneously accessed. Sharedv4 volumes are for providing simultaneous (concurrent or shared) access to a volume from multiple hosts at the same time.
  • You do not necessarily need a replication factor of greater than 1 on your volume in order for it to be shared. Even a volume with a replication factor of 1 can be shared on as many nodes as there are in your cluster.
  • IOPS might be misleading when using sharedv4 volumes due to batching of small blocksize I/Os into a larger one before I/O reaches the pxd device. Bandwidth is more consistent.

A typical pattern is for a single container to have one or more volumes. Conversely, many scenarios would benefit from multiple containers being able to access the same volume, possibly from different hosts. Accordingly, the shared volume feature enables a single volume to be read/write accessible by multiple containers. Example use cases include:

  • A technical computing workload sourcing its input and writing its output to a sharedv4 volume.
  • Scaling a number of Wordpress containers based on load while managing a single sharedv4 volume.
  • Collecting logs to a central location.
note

Usage of sharedv4 volumes for databases is not recommended because they have a small metadata overhead. Additionally, typical databases do not support concurrent writes to the underlying database at the same time.

Sharedv4 failover and failover strategy​

When the node which is exporting the sharedv4 or sharedv4 service volume becomes unavailable, there is a sharedv4 failover. After failover, the volume is exported from another node which has a replica of the volume.

Failover is handled slightly differently for sharedv4 volumes than for sharedv4 service volumes:

  • When a sharedv4 volume fails over, all of the application pods are restarted.
  • For sharedv4 service volumes, only a subset of the pods need to be restarted. These are the pods that were running on the 2 nodes involved in failover: the node that became unavailable, and the node that started exporting the replica of the volume. The pods running on the other nodes do not need to be restarted.

The failover strategy determines how quickly the failover will start after detecting that the node exporting the volume has become unavailable. The normal strategy waits for a longer duration than the aggressive strategy.

Sharedv4 volumes​

The default failover strategy for sharedv4 volumes is normal. This gives the unavailable node more time to come back up after a transient issue. If the node comes back up during the grace period allowed by the normal failover strategy, there is no need to restart the application pods.

If an application with a sharedv4 volume is able to recover quickly after a restart, it may be more appropriate to use the aggressive failover strategy even for a sharedv4 volume.

Sharedv4 service volumes​

The default failover strategy for sharedv4 service volumes is aggressive, because these volumes are able to fail over without restarting all the application pods.

These defaults can be changed in the following ways:

Sharedv4 service volume hyperconvergence​

When you set the stork.libopenstorage.org/preferRemoteNode parameter in the StorageClass as false, Stork will deactivate anti-hyperconvergence for sharedv4 service volumes generated with this StorageClass, and the value of the stork.libopenstorage.org/preferRemoteNodeOnly parameter will be ignored.

note

The stork.libopenstorage.org/preferRemoteNode parameter is supported from the Stork 23.11.0 and newer versions, and the default setting for this parameter is true.

Sharedv4 service pod anti-hyperconvergence​

If you want to prevent pods from needing to bounce upon NFS server failover for sharedv4 service volumes, you would have to use NFS mountpoints on nodes instead of having pods running on the node with the volume attached as a direct bind mount.

By default, the Stork scheduler places application pods on nodes where sharedv4 volume replicas do not exist, if such nodes are available. This configuration is known as anti-hyperconvergence, meaning that pods are positioned on different nodes from their volume replicas. In other words, this can be described as the pods using sharedv4 volumes being anti-hyperconverged with respect to their volume replicas.

note

You can force a pod using sharedV4 service volumes to be scheduled only on non replica nodes by specifying stork.libopenstorage.org/preferRemoteNodeOnly: "true" as a StorageClass parameter. This parameter will strictly enforce this behavior, and application pods will not come up if a valid node is not found.

Delete volumes​

You can delete a specific volume using the pxctl volume delete command. For example, the following command deletes the myOldVol volume:

pxctl volume delete myOldVol
Delete volume 'myOldVol', proceed ? (Y/N): y
Volume myOldVol successfully deleted.

Import volumes​

You can import files from a directory into an existing volume. The existing files on the volume are retained or overwritten.

For example, the following command imports files from the /path/to/files directory into myVol:

pxctl volume import --src /path/to/files myVol
Starting import of  data from /path/to/files into volume myVol...Beginning data transfer from /path/to/files myVol
Imported Bytes :   0% [>---------------------------------------------------------------------------------------------------------------------------------------] 14ms
Imported Files :   0% [>---------------------------------------------------------------------------------------------------------------------------------------] 16ms

Volume imported successfully

Inspect volumes​

For more information about inspecting your Portworx volumes, see:

Inspect volumes

List volumes​

The following command lists all volumes within a cluster:

pxctl volume list
ID			NAME		SIZE	HA	SHARED	ENCRYPTED	IO_PRIORITY	STATUS				SNAP-ENABLED
951679824907051932	objectstorevol	10 GiB	1	no	no		LOW		up - attached on 192.168.99.101	no
810987143668394709	testvol		1 GiB	1	no	no		LOW		up - detached			no
1047941676033657203	testvol2	1 GiB	1	no	no		LOW		up - detached			no
800735594334174869	testvol3	1 GiB	1	no	no		LOW		up - detached			no

List volumes in a drive​

The following command displays details about volumes that are located on a specific drive:

pxctl volume list --cloud-drive-id "[datastore-xxxxx] fcd/<file-name.vmdk>"
ID                NAME      SIZE      HA    SHARED  ENCRYPTED   PROXY-VOLUME    IO_PRIORITY   STATUS          SNAP-ENABLED
<volume-id>	testvol   10 GiB    2     no      no          no              LOW           up - attached   no

This functionality is useful for administrators who need to audit, manage, or troubleshoot storage resources by correlating volumes with their physical or logical storage locations.

List volumes in trash can​

When the trash can is enabled, you can list volumes in the trash can with the following command:

pxctl volume list --trashcan

This displays output similar to the following:

DELETE TIME                   ID                  NAME                  SIZE   HA  SHARED  ENCRYPTED  IO_PRIORITY  STATUS         DELETE_TIMER
Tue Mar 29 21:51:16 UTC 2022  780196670250220779  newvol-tc-1648590676  1 GiB  1   no      no         LOW          up - detached  9m33s

In the sample output above, the trash can volume name is in the format <original-vol-name>-tc-<original-vol-id>.

  • To learn how to enable the volume trash can feature on a cluster, see Volume trash can.

Locate volumes​

The pxctl volume locate command displays the mounted location of a volume in the containers running on the node:

pxctl volume locate 794896567744466024
host mounted:
  /directory1
  /directory2

In the above example, the 794896567744466024 volume is mounted in two containers through the /directory1 and /directory2 mount points.

Create volume snapshots​

Snapshots are efficient point-in-time read-only copies of volumes. Once created, you can use a snapshot to read data, restore data, and to make clones from a given snapshot.

Under the hood, snapshots are using a copy-on-write technique, so that they store only the modified data. This way, snapshots significantly reduce the consumption of resources.

Snapshots can be created explicitly by running the pxctl volume snapshot create command (called henceforth user created snapshots) or through a schedule that is set on the volume.

Here's an example of how to create a snapshot:

pxctl volume snapshot create --name mysnap --label color=blue,fabric=wool myvol
Volume snap successful: 234835613696329810

The string of digits in the output is the volume ID of the new snapshot. You can use this ID(234835613696329810) or the name(mysnap), to refer to the snapshot in subsequent pxctl commands.

The label values allow you to tag the snapshot with descriptive information of your choosing. You can use them to filter the output of the pxctl volume list command.

There is an implementation limit of 64 snapshots per volume.

Snapshots are read-only. To restore a volume from a snapshot, use the pxctl volume restore command.

  • For information about creating snapshots of your Portworx volumes through Kubernetes, refer to the Create and use snapshots page.

Clone volumes​

Use the pxctl volume clone command to create a volume clone from a volume or snapshot.

To view the in-built help, run the pxctl volume clone command with the --help flag.

For example, the following command creates the myvol_clone clone from the parent myvol volume:

pxctl volume clone -name myvol_clone myvol
Volume clone successful: 55898055774694370
  • For information about creating a clone from a snapshot through Kubernetes, refer to the On-demand snapshots page.

Restore a volume​

In order to restore a volume from snapshot use the pxctl volume restore command:

/opt/pwx/bin/pxctl volume restore -h
Restore volume from snapshot

Usage:
  pxctl volume restore [flags]

Aliases:
  restore, r

Examples:
pxctl volume restore [flags] volName

Flags:
  -h, --help              help for restore
  -s, --snapshot string   snapshot-name-or-ID

Global Flags:
      --ca string            path to root certificate for ssl usage
      --cert string          path to client certificate for ssl usage
      --color                output with color coding
      --config string        config file (default is $HOME/.pxctl.yaml)
      --context string       context name that overrides the current auth context
  -j, --json                 output in json
      --key string           path to client key for ssl usage
      --output-type string   use "wide" to show more details
      --raw                  raw CLI output for instrumentation
      --ssl                  ssl enabled for portworx

In the below example parent volume myvol is restored from its snapshot mysnap. Make sure volume is detached in order to restore from the snapshot.

pxctl volume restore --snapshot mysnap myvol
Successfully started restoring volume myvol from mysnap.

To restore a volume from the trash can, specify the --trashcan flag:

pxctl volume restore --trashcan trashedvol myvol
Successfully started restoring volume myvol from trashedvol.
  • To learn how to enable the volume trash can feature on a cluster, see Volume trash can.
  • For information about restoring a Portworx volume with data from a snapshot through Kubernetes, refer to the Restore snapshots page.

Update the snap interval of a volume​

Please see the documentation for [snapshots] (/reference/cli/snapshots) for more details.

  • For information about creating scheduled snapshots of a Portworx volume through Kubernetes, refer to the Scheduled snapshots page.

Show volume stats​

The pxctl volume stat command displays the real-time read/write IO throughput:

pxctl volume stats mvVol
TS			Bytes Read	Num Reads	Bytes Written	Num Writes	IOPS		IODepth		Read Tput	Write Tput	Read Lat(usec)	Write Lat(usec)
2019-3-4:11 Hrs		0 B		0		0 B		0		0		0		0 B/s		0 B/s		0		0

Manage volume access rules​

Using pxctl, you can manage your volume access rules. See the volume access page for more details.

Update the replication factor of a volume​

You can use the pxctl volume ha-update to increase or decrease the replication factor of a Portworx volume. Refer to the update volumes page for more details.

Update the settings of a volume​

Using the pxctl volume update command, you can update the settings of your Portworx volumes. Refer to the updating volumes page for additional details.

Volume usage​

To get more information about the usage of your Portworx volumes, run the pxctl volume usage command with the name or the ID of your volume:

pxctl volume usage 13417687767517527

Understand copy-on-write features​

By default, Portworx uses features present in the underlying file system to take snapshots through copy-on-write and checksum storage blocks.

When using the copy-on-write feature to take snapshots, overwriting a block does not update it in place. Instead, every overwrite allocates or updates a new block, and the filesystem metadata is updated to point to this new block. This technique is called redirect-on-write. When using this feature, a block overwrite almost always involves block updates in multiple areas:

  • the target block
  • any linked indirect file blocks
  • filesystem metadata blocks
  • filesystem metadata indirect file blocks

In a background process, separate from the overwrite operation, the old block is freed only if it is not referred by a snapshot or clone. In addition to copy-on-write, the file system checksums all blocks to detect lost writes and stores the checksum values in a different location away from their associated data.

While these combined features increase the integrity of the data stored on the filesystem, they also increase the read and write overhead on the drives that use them. This slows down performance and increases latency during file operations.

Depending on your use-case, you can trade off the integrity copy-on-write features offer for increased performance and lower latency. You can do this on a per-volume basis using the pxctl command.

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