instruction: Explain Persistent Volumes
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  Persistent Volumes
  This document describes
  persistent volumes
  in Kubernetes. Familiarity with
  volumes
  StorageClasses
  VolumeAttributesClasses
  is suggested.
  Introduction
  Managing storage is a distinct problem from managing compute instances.
  The PersistentVolume subsystem provides an API for users and administrators
  that abstracts details of how storage is provided from how it is consumed.
  To do this, we introduce two new API resources: PersistentVolume and PersistentVolumeClaim.
  PersistentVolume
  (PV) is a piece of storage in the cluster that has been
  provisioned by an administrator or dynamically provisioned using
  Storage Classes
  . It is a resource in
  the cluster just like a node is a cluster resource. PVs are volume plugins like
  Volumes, but have a lifecycle independent of any individual Pod that uses the PV.
  This API object captures the details of the implementation of the storage, be that
  NFS, iSCSI, or a cloud-provider-specific storage system.
  PersistentVolumeClaim
  (PVC) is a request for storage by a user. It is similar
  to a Pod. Pods consume node resources and PVCs consume PV resources. Pods can
  request specific levels of resources (CPU and Memory). Claims can request specific
  size and access modes (e.g., they can be mounted ReadWriteOnce, ReadOnlyMany,
  ReadWriteMany, or ReadWriteOncePod, see
  AccessModes
  While PersistentVolumeClaims allow a user to consume abstract storage resources,
  it is common that users need PersistentVolumes with varying properties, such as
  performance, for different problems. Cluster administrators need to be able to
  offer a variety of PersistentVolumes that differ in more ways than size and access
  modes, without exposing users to the details of how those volumes are implemented.
  For these needs, there is the
  StorageClass
  resource.
  See the
  detailed walkthrough with working examples
  Lifecycle of a volume and claim
  PVs are resources in the cluster. PVCs are requests for those resources and also act
  as claim checks to the resource. The interaction between PVs and PVCs follows this lifecycle:
  Provisioning
  There are two ways PVs may be provisioned: statically or dynamically.
  Static
  A cluster administrator creates a number of PVs. They carry the details of the
  real storage, which is available for use by cluster users. They exist in the
  Kubernetes API and are available for consumption.
  Dynamic
  When none of the static PVs the administrator created match a user's PersistentVolumeClaim,
  the cluster may try to dynamically provision a volume specially for the PVC.
  This provisioning is based on StorageClasses: the PVC must request a
  storage class
  the administrator must have created and configured that class for dynamic
  provisioning to occur. Claims that request the class
  effectively disable
  dynamic provisioning for themselves.
  To enable dynamic storage provisioning based on storage class, the cluster administrator
  needs to enable the
  DefaultStorageClass
  admission controller
  on the API server. This can be done, for example, by ensuring that
  DefaultStorageClass
  among the comma-delimited, ordered list of values for the
  --enable-admission-plugins
  flag of
  the API server component. For more information on API server command-line flags,
  check
  kube-apiserver
  documentation.
  Binding
  A user creates, or in the case of dynamic provisioning, has already created,
  a PersistentVolumeClaim with a specific amount of storage requested and with
  certain access modes. A control loop in the control plane watches for new PVCs, finds
  a matching PV (if possible), and binds them together. If a PV was dynamically
  provisioned for a new PVC, the loop will always bind that PV to the PVC. Otherwise,
  the user will always get at least what they asked for, but the volume may be in
  excess of what was requested. Once bound, PersistentVolumeClaim binds are exclusive,
  regardless of how they were bound. A PVC to PV binding is a one-to-one mapping,
  using a ClaimRef which is a bi-directional binding between the PersistentVolume
  and the PersistentVolumeClaim.
  Claims will remain unbound indefinitely if a matching volume does not exist.
  Claims will be bound as matching volumes become available. For example, a
  cluster provisioned with many 50Gi PVs would not match a PVC requesting 100Gi.
  The PVC can be bound when a 100Gi PV is added to the cluster.
  Using
  Pods use claims as volumes. The cluster inspects the claim to find the bound
  volume and mounts that volume for a Pod. For volumes that support multiple
  access modes, the user specifies which mode is desired when using their claim
  as a volume in a Pod.
  Once a user has a claim and that claim is bound, the bound PV belongs to the
  user for as long as they need it. Users schedule Pods and access their claimed
  PVs by including a
  persistentVolumeClaim
  section in a Pod's
  volumes
  block.
  Claims As Volumes
  for more details on this.
  Storage Object in Use Protection
  The purpose of the Storage Object in Use Protection feature is to ensure that
  PersistentVolumeClaims (PVCs) in active use by a Pod and PersistentVolume (PVs)
  that are bound to PVCs are not removed from the system, as this may result in data loss.
  Note:
  PVC is in active use by a Pod when a Pod object exists that is using the PVC.
  If a user deletes a PVC in active use by a Pod, the PVC is not removed immediately.
  PVC removal is postponed until the PVC is no longer actively used by any Pods. Also,
  if an admin deletes a PV that is bound to a PVC, the PV is not removed immediately.
  PV removal is postponed until the PV is no longer bound to a PVC.
  You can see that a PVC is protected when the PVC's status is
  Terminating
  and the
  Finalizers
  list includes
  kubernetes.io/pvc-protection
  kubectl describe pvc hostpath
  Name: hostpath
  Namespace: default
  StorageClass: example-hostpath
  Status: Terminating
  Volume:
  Labels: <none>
  Annotations: volume.beta.kubernetes.io/storage-class
  example-hostpath
  volume.beta.kubernetes.io/storage-provisioner
  example.com/hostpath
  Finalizers:
  kubernetes.io/pvc-protection
  You can see that a PV is protected when the PV's status is
  Terminating
  Finalizers
  list includes
  kubernetes.io/pv-protection
  too:
  kubectl describe pv task-pv-volume
  Name: task-pv-volume
  Labels:
  type
  local
  Annotations: <none>
  Finalizers:
  kubernetes.io/pv-protection
  StorageClass: standard
  Status: Terminating
  Claim:
  Reclaim Policy: Delete
  Access Modes: RWO
  Capacity: 1Gi
  Message:
  Source:
  Type: HostPath
  bare host directory volume
  Path: /tmp/data
  HostPathType:
  Events: <none>
  Reclaiming
  When a user is done with their volume, they can delete the PVC objects from the
  API that allows reclamation of the resource. The reclaim policy for a PersistentVolume
  tells the cluster what to do with the volume after it has been released of its claim.
  Currently, volumes can either be Retained, Recycled, or Deleted.
  Retain
  Retain
  reclaim policy allows for manual reclamation of the resource.
  When the PersistentVolumeClaim is deleted, the PersistentVolume still exists
  and the volume is considered "released". But it is not yet available for
  another claim because the previous claimant's data remains on the volume.
  An administrator can manually reclaim the volume with the following steps.
  Delete the PersistentVolume. The associated storage asset in external infrastructure
  still exists after the PV is deleted.
  Manually clean up the data on the associated storage asset accordingly.
  Manually delete the associated storage asset.
  If you want to reuse the same storage asset, create a new PersistentVolume with
  the same storage asset definition.
  Delete
  For volume plugins that support the
  Delete
  reclaim policy, deletion removes
  both the PersistentVolume object from Kubernetes, as well as the associated
  storage asset in the external infrastructure. Volumes that were dynamically provisioned
  inherit the
  reclaim policy of their StorageClass
  , which
  defaults to
  Delete
  . The administrator should configure the StorageClass
  according to users' expectations; otherwise, the PV must be edited or
  patched after it is created. See
  Change the Reclaim Policy of a PersistentVolume
  Recycle
  Warning:
  Recycle
  reclaim policy is deprecated. Instead, the recommended approach
  is to use dynamic provisioning.
  If supported by the underlying volume plugin, the
  Recycle
  reclaim policy performs
  a basic scrub (
  rm -rf /thevolume/*
  ) on the volume and makes it available again for a new claim.
  However, an administrator can configure a custom recycler Pod template using
  the Kubernetes controller manager command line arguments as described in the
  The custom recycler Pod template must contain a
  volumes
  specification, as
  shown in the example below:
  apiVersion
  kind
  metadata
  name
  pv-recycler
  namespace
  default
  spec
  restartPolicy
  Never
  volumes
  name
  hostPath
  path
  /any/path/it/will/be/replaced
  containers
  name
  pv-recycler
  image
  "registry.k8s.io/busybox"
  command
  "/bin/sh"
  "-c"
  "test -e /scrub && rm -rf /scrub/..?* /scrub/.[!.]* /scrub/* && test -z \"$(ls -A /scrub)\" || exit 1"
  volumeMounts
  name
  mountPath
  /scrub
  However, the particular path specified in the custom recycler Pod template in the
  volumes
  part is replaced with the particular path of the volume that is being recycled.
  PersistentVolume deletion protection finalizer
  FEATURE STATE:
  Kubernetes v1.31 [beta]
  (enabled by default: true)
  Finalizers can be added on a PersistentVolume to ensure that PersistentVolumes
  having
  Delete
  reclaim policy are deleted only after the backing storage are deleted.
  The finalizer
  external-provisioner.volume.kubernetes.io/finalizer
  (introduced
  in v1.31) is added to both dynamically provisioned and statically provisioned
  CSI volumes.
  The finalizer
  kubernetes.io/pv-controller
  (introduced in v1.31) is added to
  dynamically provisioned in-tree plugin volumes and skipped for statically
  provisioned in-tree plugin volumes.
  The following is an example of dynamically provisioned in-tree plugin volume:
  kubectl describe pv pvc-74a498d6-3929-47e8-8c02-078c1ece4d78
  Name: pvc-74a498d6-3929-47e8-8c02-078c1ece4d78
  Labels: <none>
  Annotations: kubernetes.io/createdby: vsphere-volume-dynamic-provisioner
  pv.kubernetes.io/bound-by-controller: yes
  pv.kubernetes.io/provisioned-by: kubernetes.io/vsphere-volume
  Finalizers:
  kubernetes.io/pv-protection kubernetes.io/pv-controller
  StorageClass: vcp-sc
  Status: Bound
  Claim: default/vcp-pvc-1
  Reclaim Policy: Delete
  Access Modes: RWO
  VolumeMode: Filesystem
  Capacity: 1Gi
  Node Affinity: <none>
  Message:
  Source:
  Type: vSphereVolume
  a Persistent Disk resource in vSphere
  VolumePath:
  vsanDatastore
  d49c4a62-166f-ce12-c464-020077ba5d46/kubernetes-dynamic-pvc-74a498d6-3929-47e8-8c02-078c1ece4d78.vmdk
  FSType: ext4
  StoragePolicyName: vSAN Default Storage Policy
  Events: <none>
  The finalizer
  external-provisioner.volume.kubernetes.io/finalizer
  is added for CSI volumes.
  The following is an example:
  Name: pvc-2f0bab97-85a8-4552-8044-eb8be45cf48d
  Labels: <none>
  Annotations: pv.kubernetes.io/provisioned-by: csi.vsphere.vmware.com
  Finalizers:
  kubernetes.io/pv-protection external-provisioner.volume.kubernetes.io/finalizer
  StorageClass: fast
  Status: Bound
  Claim: demo-app/nginx-logs
  Reclaim Policy: Delete
  Access Modes: RWO
  VolumeMode: Filesystem
  Capacity: 200Mi
  Node Affinity: <none>
  Message:
  Source:
  Type: CSI
  a Container Storage Interface
  volume
  source
  Driver: csi.vsphere.vmware.com
  FSType: ext4
  VolumeHandle: 44830fa8-79b4-406b-8b58-621ba25353fd
  ReadOnly:
  false
  VolumeAttributes: storage.kubernetes.io/csiProvisionerIdentity
  1648442357185-8081-csi.vsphere.vmware.com
  type
  vSphere CNS Block Volume
  Events: <none>
  When the
  CSIMigration{provider}
  feature flag is enabled for a specific in-tree volume plugin,
  kubernetes.io/pv-controller
  finalizer is replaced by the
  external-provisioner.volume.kubernetes.io/finalizer
  finalizer.
  The finalizers ensure that the PV object is removed only after the volume is deleted
  from the storage backend provided the reclaim policy of the PV is
  Delete
  . This
  also ensures that the volume is deleted from storage backend irrespective of the
  order of deletion of PV and PVC.
  Reserving a PersistentVolume
  The control plane can
  bind PersistentVolumeClaims to matching PersistentVolumes
  in the cluster. However, if you want a PVC to bind to a specific PV, you need to pre-bind them.
  By specifying a PersistentVolume in a PersistentVolumeClaim, you declare a binding
  between that specific PV and PVC. If the PersistentVolume exists and has not reserved
  PersistentVolumeClaims through its
  claimRef
  field, then the PersistentVolume and
  PersistentVolumeClaim will be bound.
  The binding happens regardless of some volume matching criteria, including node affinity.
  The control plane still checks that
  storage class
  access modes, and requested storage size are valid.
  apiVersion
  kind
  PersistentVolumeClaim
  metadata
  name
  foo-pvc
  namespace
  spec
  storageClassName
  # Empty string must be explicitly set otherwise default StorageClass will be set
  volumeName
  foo-pv
  This method does not guarantee any binding privileges to the PersistentVolume.
  If other PersistentVolumeClaims could use the PV that you specify, you first
  need to reserve that storage volume. Specify the relevant PersistentVolumeClaim
  in the
  claimRef
  field of the PV so that other PVCs can not bind to it.
  apiVersion
  kind
  PersistentVolume
  metadata
  name
  foo-pv
  spec
  storageClassName
  claimRef
  name
  foo-pvc
  namespace
  This is useful if you want to consume PersistentVolumes that have their
  persistentVolumeReclaimPolicy
  Retain
  , including cases where you are reusing an existing PV.
  Expanding Persistent Volumes Claims
  FEATURE STATE:
  Kubernetes v1.24 [stable]
  Support for expanding PersistentVolumeClaims (PVCs) is enabled by default. You can expand
  the following types of volumes:
  azureFile (deprecated)
  flexVolume (deprecated)
  rbd (deprecated)
  portworxVolume (deprecated)
  You can only expand a PVC if its storage class's
  allowVolumeExpansion
  field is set to true.
  apiVersion
  storage.k8s.io/v1
  kind
  StorageClass
  metadata
  name
  example-vol-default
  provisioner
  vendor-name.example/magicstorage
  parameters
  resturl
  "http://192.168.10.100:8080"
  restuser
  secretNamespace
  secretName
  allowVolumeExpansion
  true
  To request a larger volume for a PVC, edit the PVC object and specify a larger
  size. This triggers expansion of the volume that backs the underlying PersistentVolume. A
  new PersistentVolume is never created to satisfy the claim. Instead, an existing volume is resized.
  Warning:
  Directly editing the size of a PersistentVolume can prevent an automatic resize of that volume.
  If you edit the capacity of a PersistentVolume, and then edit the
  .spec
  of a matching
  PersistentVolumeClaim to make the size of the PersistentVolumeClaim match the PersistentVolume,
  then no storage resize happens.
  The Kubernetes control plane will see that the desired state of both resources matches,
  conclude that the backing volume size has been manually
  increased and that no resize is necessary.
  CSI Volume expansion
  FEATURE STATE:
  Kubernetes v1.24 [stable]
  Support for expanding CSI volumes is enabled by default but it also requires a
  specific CSI driver to support volume expansion. Refer to documentation of the
  specific CSI driver for more information.
  Resizing a volume containing a file system
  You can only resize volumes containing a file system if the file system is XFS, Ext3, or Ext4.
  When a volume contains a file system, the file system is only resized when a new Pod is using
  the PersistentVolumeClaim in
  ReadWrite
  mode. File system expansion is either done when a Pod is starting up
  or when a Pod is running and the underlying file system supports online expansion.
  FlexVolumes (deprecated since Kubernetes v1.23) allow resize if the driver is configured with the
  RequiresFSResize
  capability to
  true
  . The FlexVolume can be resized on Pod restart.
  Resizing an in-use PersistentVolumeClaim
  FEATURE STATE:
  Kubernetes v1.24 [stable]
  In this case, you don't need to delete and recreate a Pod or deployment that is using an existing PVC.
  Any in-use PVC automatically becomes available to its Pod as soon as its file system has been expanded.
  This feature has no effect on PVCs that are not in use by a Pod or deployment. You must create a Pod that
  uses the PVC before the expansion can complete.
  Similar to other volume types - FlexVolume volumes can also be expanded when in-use by a Pod.
  Note:
  FlexVolume resize is possible only when the underlying driver supports resize.
  Recovering from Failure when Expanding Volumes
  If a user specifies a new size that is too big to be satisfied by underlying
  storage system, expansion of PVC will be continuously retried until user or
  cluster administrator takes some action. This can be undesirable and hence
  Kubernetes provides following methods of recovering from such failures.
  Manually with Cluster Administrator access
  By requesting expansion to smaller size
  If expanding underlying storage fails, the cluster administrator can manually
  recover the Persistent Volume Claim (PVC) state and cancel the resize requests.
  Otherwise, the resize requests are continuously retried by the controller without
  administrator intervention.
  Mark the PersistentVolume(PV) that is bound to the PersistentVolumeClaim(PVC)
  with
  Retain
  reclaim policy.
  Delete the PVC. Since PV has
  Retain
  reclaim policy - we will not lose any data
  when we recreate the PVC.
  Delete the
  claimRef
  entry from PV specs, so as new PVC can bind to it.
  This should make the PV
  Available
  Re-create the PVC with smaller size than PV and set
  volumeName
  field of the
  PVC to the name of the PV. This should bind new PVC to existing PV.
  Don't forget to restore the reclaim policy of the PV.
  FEATURE STATE:
  Kubernetes v1.23 [alpha]
  Note:
  Recovery from failing PVC expansion by users is available as an alpha feature
  since Kubernetes 1.23. The
  RecoverVolumeExpansionFailure
  feature must be
  enabled for this feature to work. Refer to the
  feature gate
  documentation for more information.
  If the feature gates
  RecoverVolumeExpansionFailure
  enabled in your cluster, and expansion has failed for a PVC, you can retry expansion with a
  smaller size than the previously requested value. To request a new expansion attempt with a
  smaller proposed size, edit
  .spec.resources
  for that PVC and choose a value that is less than the
  value you previously tried.
  This is useful if expansion to a higher value did not succeed because of capacity constraint.
  If that has happened, or you suspect that it might have, you can retry expansion by specifying a
  size that is within the capacity limits of underlying storage provider. You can monitor status of
  resize operation by watching
  .status.allocatedResourceStatuses
  and events on the PVC.
  Note that,
  although you can specify a lower amount of storage than what was requested previously,
  the new value must still be higher than
  .status.capacity
  Kubernetes does not support shrinking a PVC to less than its current size.
  Types of Persistent Volumes
  PersistentVolume types are implemented as plugins. Kubernetes currently supports the following plugins:
  - Container Storage Interface (CSI)
  - Fibre Channel (FC) storage
  hostPath
  - HostPath volume
  (for single node testing only; WILL NOT WORK in a multi-node cluster;
  consider using
  local
  volume instead)
  iscsi
  - iSCSI (SCSI over IP) storage
  local
  - local storage devices
  mounted on nodes.
  - Network File System (NFS) storage
  The following types of PersistentVolume are deprecated but still available.
  If you are using these volume types except for
  flexVolume
  cephfs
  please install corresponding CSI drivers.
  awsElasticBlockStore
  - AWS Elastic Block Store (EBS)
  migration on by default
  starting v1.23)
  azureDisk
  - Azure Disk
  migration on by default
  starting v1.23)
  azureFile
  - Azure File
  migration on by default
  starting v1.24)
  cinder
  - Cinder (OpenStack block storage)
  migration on by default
  starting v1.21)
  flexVolume
  - FlexVolume
  deprecated
  starting v1.23, no migration plan and no plan to remove support)
  gcePersistentDisk
  - GCE Persistent Disk
  migration on by default
  starting v1.23)
  portworxVolume
  - Portworx volume
  migration on by default
  starting v1.31)
  vsphereVolume
  - vSphere VMDK volume
  migration on by default
  starting v1.25)
  Older versions of Kubernetes also supported the following in-tree PersistentVolume types:
  cephfs
  not available
  starting v1.31)
  flocker
  - Flocker storage.
  not available
  starting v1.25)
  photonPersistentDisk
  - Photon controller persistent disk.
  not available
  starting v1.15)
  quobyte
  - Quobyte volume.
  not available
  starting v1.25)
  - Rados Block Device (RBD) volume
  not available
  starting v1.31)
  scaleIO
  - ScaleIO volume.
  not available
  starting v1.21)
  storageos
  - StorageOS volume.
  not available
  starting v1.25)
  Persistent Volumes
  Each PV contains a spec and status, which is the specification and status of the volume.
  The name of a PersistentVolume object must be a valid
  DNS subdomain name
  apiVersion
  kind
  PersistentVolume
  metadata
  name
  pv0003
  spec
  capacity
  storage
  volumeMode
  Filesystem
  accessModes
  - ReadWriteOnce
  persistentVolumeReclaimPolicy
  Recycle
  storageClassName
  slow
  mountOptions
  - hard
  - nfsvers=4.1
  path
  /tmp
  server
  Note:
  Helper programs relating to the volume type may be required for consumption of
  a PersistentVolume within a cluster. In this example, the PersistentVolume is
  of type NFS and the helper program /sbin/mount.nfs is required to support the
  mounting of NFS filesystems.
  Capacity
  Generally, a PV will have a specific storage capacity. This is set using the PV's
  capacity
  attribute which is a
  Quantity
  value.
  Currently, storage size is the only resource that can be set or requested.
  Future attributes may include IOPS, throughput, etc.
  Volume Mode
  FEATURE STATE:
  Kubernetes v1.18 [stable]
  Kubernetes supports two
  volumeModes
  of PersistentVolumes:
  Filesystem
  Block
  volumeMode
  is an optional API parameter.
  Filesystem
  is the default mode used when
  volumeMode
  parameter is omitted.
  A volume with
  volumeMode: Filesystem
  mounted
  into Pods into a directory. If the volume
  is backed by a block device and the device is empty, Kubernetes creates a filesystem
  on the device before mounting it for the first time.
  You can set the value of
  volumeMode
  Block
  to use a volume as a raw block device.
  Such volume is presented into a Pod as a block device, without any filesystem on it.
  This mode is useful to provide a Pod the fastest possible way to access a volume, without
  any filesystem layer between the Pod and the volume. On the other hand, the application
  running in the Pod must know how to handle a raw block device.
  Raw Block Volume Support
  for an example on how to use a volume with
  volumeMode: Block
  in a Pod.
  Access Modes
  A PersistentVolume can be mounted on a host in any way supported by the resource
  provider. As shown in the table below, providers will have different capabilities
  and each PV's access modes are set to the specific modes supported by that particular
  volume. For example, NFS can support multiple read/write clients, but a specific
  NFS PV might be exported on the server as read-only. Each PV gets its own set of
  access modes describing that specific PV's capabilities.
  The access modes are:
  ReadWriteOnce
  the volume can be mounted as read-write by a single node. ReadWriteOnce access
  mode still can allow multiple pods to access the volume when the pods are
  running on the same node. For single pod access, please see ReadWriteOncePod.
  ReadOnlyMany
  the volume can be mounted as read-only by many nodes.
  ReadWriteMany
  the volume can be mounted as read-write by many nodes.
  ReadWriteOncePod
  FEATURE STATE:
  Kubernetes v1.29 [stable]
  the volume can be mounted as read-write by a single Pod. Use ReadWriteOncePod
  access mode if you want to ensure that only one pod across the whole cluster can
  read that PVC or write to it.
  Note:
  ReadWriteOncePod
  access mode is only supported for
  volumes and Kubernetes version
  1.22+. To use this feature you will need to update the following
  CSI sidecars
  to these versions or greater:
  csi-provisioner:v3.0.0+
  csi-attacher:v3.3.0+
  csi-resizer:v1.3.0+
  In the CLI, the access modes are abbreviated to:
  RWO - ReadWriteOnce
  ROX - ReadOnlyMany
  RWX - ReadWriteMany
  RWOP - ReadWriteOncePod
  Note:
  Kubernetes uses volume access modes to match PersistentVolumeClaims and PersistentVolumes.
  In some cases, the volume access modes also constrain where the PersistentVolume can be mounted.
  Volume access modes do
  enforce write protection once the storage has been mounted.
  Even if the access modes are specified as ReadWriteOnce, ReadOnlyMany, or ReadWriteMany,
  they don't set any constraints on the volume. For example, even if a PersistentVolume is
  created as ReadOnlyMany, it is no guarantee that it will be read-only. If the access modes
  are specified as ReadWriteOncePod, the volume is constrained and can be mounted on only a single Pod.
  Important!
  A volume can only be mounted using one access mode at a time,
  even if it supports many.
  Volume Plugin
  ReadWriteOnce
  ReadOnlyMany
  ReadWriteMany
  ReadWriteOncePod
  AzureFile
  CephFS
  depends on the driver
  depends on the driver
  depends on the driver
  depends on the driver
  FlexVolume
  depends on the driver
  HostPath
  iSCSI
  VsphereVolume
  - (works when Pods are collocated)
  PortworxVolume
  Class
  A PV can have a class, which is specified by setting the
  storageClassName
  attribute to the name of a
  StorageClass
  A PV of a particular class can only be bound to PVCs requesting
  that class. A PV with no
  storageClassName
  has no class and can only be bound
  to PVCs that request no particular class.
  In the past, the annotation
  volume.beta.kubernetes.io/storage-class
  was used instead
  of the
  storageClassName
  attribute. This annotation is still working; however,
  it will become fully deprecated in a future Kubernetes release.
  Reclaim Policy
  Current reclaim policies are:
  Retain -- manual reclamation
  Recycle -- basic scrub (
  rm -rf /thevolume/*
  Delete -- delete the volume
  For Kubernetes 1.31, only
  hostPath
  volume types support recycling.
  Mount Options
  A Kubernetes administrator can specify additional mount options for when a
  Persistent Volume is mounted on a node.
  Note:
  Not all Persistent Volume types support mount options.
  The following volume types support mount options:
  azureFile
  cephfs
  deprecated
  in v1.28)
  cinder
  deprecated
  in v1.18)
  iscsi
  deprecated
  in v1.28)
  vsphereVolume
  Mount options are not validated. If a mount option is invalid, the mount fails.
  In the past, the annotation
  volume.beta.kubernetes.io/mount-options
  was used instead
  of the
  mountOptions
  attribute. This annotation is still working; however,
  it will become fully deprecated in a future Kubernetes release.
  Node Affinity
  Note:
  For most volume types, you do not need to set this field.
  You need to explicitly set this for
  local
  volumes.
  A PV can specify node affinity to define constraints that limit what nodes this
  volume can be accessed from. Pods that use a PV will only be scheduled to nodes
  that are selected by the node affinity. To specify node affinity, set
  nodeAffinity
  in the
  .spec
  of a PV. The
  PersistentVolume
  API reference has more details on this field.
  Phase
  A PersistentVolume will be in one of the following phases:
  Available
  a free resource that is not yet bound to a claim
  Bound
  the volume is bound to a claim
  Released
  the claim has been deleted, but the associated storage resource is not yet reclaimed by the cluster
  Failed
  the volume has failed its (automated) reclamation
  You can see the name of the PVC bound to the PV using
  kubectl describe persistentvolume <name>
  Phase transition timestamp
  FEATURE STATE:
  Kubernetes v1.31 [stable]
  (enabled by default: true)
  .status
  field for a PersistentVolume can include an alpha
  lastPhaseTransitionTime
  field. This field records
  the timestamp of when the volume last transitioned its phase. For newly created
  volumes the phase is set to
  Pending
  lastPhaseTransitionTime
  is set to
  the current time.
  PersistentVolumeClaims
  Each PVC contains a spec and status, which is the specification and status of the claim.
  The name of a PersistentVolumeClaim object must be a valid
  DNS subdomain name
  apiVersion
  kind
  PersistentVolumeClaim
  metadata
  name
  myclaim
  spec
  accessModes
  - ReadWriteOnce
  volumeMode
  Filesystem
  resources
  requests
  storage
  storageClassName
  slow
  selector
  matchLabels
  release
  "stable"
  matchExpressions
  key: environment, operator: In, values
  [dev]}
  Access Modes
  Claims use
  the same conventions as volumes
  when requesting
  storage with specific access modes.
  Volume Modes
  Claims use
  the same convention as volumes
  to indicate the
  consumption of the volume as either a filesystem or block device.
  Resources
  Claims, like Pods, can request specific quantities of a resource. In this case,
  the request is for storage. The same
  resource model
  applies to both volumes and claims.
  Selector
  Claims can specify a
  label selector
  to further filter the set of volumes. Only the volumes whose labels match the selector
  can be bound to the claim. The selector can consist of two fields:
  matchLabels
  - the volume must have a label with this value
  matchExpressions
  - a list of requirements made by specifying key, list of values,
  and operator that relates the key and values. Valid operators include In, NotIn,
  Exists, and DoesNotExist.
  All of the requirements, from both
  matchLabels
  matchExpressions
  , are
  ANDed together – they must all be satisfied in order to match.
  Class
  A claim can request a particular class by specifying the name of a
  StorageClass
  using the attribute
  storageClassName
  Only PVs of the requested class, ones with the same
  storageClassName
  as the PVC, can
  be bound to the PVC.
  PVCs don't necessarily have to request a class. A PVC with its
  storageClassName
  equal to
  is always interpreted to be requesting a PV with no class, so it
  can only be bound to PVs with no class (no annotation or one set equal to
  ). A PVC with no
  storageClassName
  is not quite the same and is treated differently
  by the cluster, depending on whether the
  DefaultStorageClass
  admission plugin
  is turned on.
  If the admission plugin is turned on, the administrator may specify a
  default StorageClass. All PVCs that have no
  storageClassName
  can be bound only to
  PVs of that default. Specifying a default StorageClass is done by setting the
  annotation
  storageclass.kubernetes.io/is-default-class
  equal to
  true
  a StorageClass object. If the administrator does not specify a default, the
  cluster responds to PVC creation as if the admission plugin were turned off. If more than one
  default StorageClass is specified, the newest default is used when the
  PVC is dynamically provisioned.
  If the admission plugin is turned off, there is no notion of a default
  StorageClass. All PVCs that have
  storageClassName
  set to
  can be
  bound only to PVs that have
  storageClassName
  also set to
  However, PVCs with missing
  storageClassName
  can be updated later once
  default StorageClass becomes available. If the PVC gets updated it will no
  longer bind to PVs that have
  storageClassName
  also set to
  retroactive default StorageClass assignment
  for more details.
  Depending on installation method, a default StorageClass may be deployed
  to a Kubernetes cluster by addon manager during installation.
  When a PVC specifies a
  selector
  in addition to requesting a StorageClass,
  the requirements are ANDed together: only a PV of the requested class and with
  the requested labels may be bound to the PVC.
  Note:
  Currently, a PVC with a non-empty
  selector
  can't have a PV dynamically provisioned for it.
  In the past, the annotation
  volume.beta.kubernetes.io/storage-class
  was used instead
  storageClassName
  attribute. This annotation is still working; however,
  it won't be supported in a future Kubernetes release.
  Retroactive default StorageClass assignment
  FEATURE STATE:
  Kubernetes v1.28 [stable]
  You can create a PersistentVolumeClaim without specifying a
  storageClassName
  for the new PVC, and you can do so even when no default StorageClass exists
  in your cluster. In this case, the new PVC creates as you defined it, and the
  storageClassName
  of that PVC remains unset until default becomes available.
  When a default StorageClass becomes available, the control plane identifies any
  existing PVCs without
  storageClassName
  . For the PVCs that either have an empty
  value for
  storageClassName
  or do not have this key, the control plane then
  updates those PVCs to set
  storageClassName
  to match the new default StorageClass.
  If you have an existing PVC where the
  storageClassName
  , and you configure
  a default StorageClass, then this PVC will not get updated.
  In order to keep binding to PVs with
  storageClassName
  set to
  (while a default StorageClass is present), you need to set the
  storageClassName
  of the associated PVC to
  This behavior helps administrators change default StorageClass by removing the
  old one first and then creating or setting another one. This brief window while
  there is no default causes PVCs without
  storageClassName
  created at that time
  to not have any default, but due to the retroactive default StorageClass
  assignment this way of changing defaults is safe.
  Claims As Volumes
  Pods access storage by using the claim as a volume. Claims must exist in the
  same namespace as the Pod using the claim. The cluster finds the claim in the
  Pod's namespace and uses it to get the PersistentVolume backing the claim.
  The volume is then mounted to the host and into the Pod.
  apiVersion
  kind
  metadata
  name
  mypod
  spec
  containers
  name
  myfrontend
  image
  nginx
  volumeMounts
  mountPath
  "/var/www/html"
  name
  mypd
  volumes
  name
  mypd
  persistentVolumeClaim
  claimName
  myclaim
  A Note on Namespaces
  PersistentVolumes binds are exclusive, and since PersistentVolumeClaims are
  namespaced objects, mounting claims with "Many" modes (
  ) is only
  possible within one namespace.
  PersistentVolumes typed
  hostPath
  hostPath
  PersistentVolume uses a file or directory on the Node to emulate
  network-attached storage. See
  an example of
  hostPath
  typed volume
  Raw Block Volume Support
  FEATURE STATE:
  Kubernetes v1.18 [stable]
  The following volume plugins support raw block volumes, including dynamic provisioning where
  applicable:
  FC (Fibre Channel)
  iSCSI
  Local volume
  OpenStack Cinder
  RBD (deprecated)
  RBD (Ceph Block Device; deprecated)
  VsphereVolume
  PersistentVolume using a Raw Block Volume
  apiVersion
  kind
  PersistentVolume
  metadata
  name
  block-pv
  spec
  capacity
  storage
  10Gi
  accessModes
  - ReadWriteOnce
  volumeMode
  Block
  persistentVolumeReclaimPolicy
  Retain
  targetWWNs
  "50060e801049cfd1"
  readOnly
  false
  PersistentVolumeClaim requesting a Raw Block Volume
  apiVersion
  kind
  PersistentVolumeClaim
  metadata
  name
  block-pvc
  spec
  accessModes
  - ReadWriteOnce
  volumeMode
  Block
  resources
  requests
  storage
  10Gi
  Pod specification adding Raw Block Device path in container
  apiVersion
  kind
  metadata
  name
  pod-with-block-volume
  spec
  containers
  name
  fc-container
  image
  fedora:26
  command
  "/bin/sh"
  "-c"
  args
  "tail -f /dev/"
  volumeDevices
  name
  data
  devicePath
  /dev/xvda
  volumes
  name
  data
  persistentVolumeClaim
  claimName
  block-pvc
  Note:
  When adding a raw block device for a Pod, you specify the device path in the
  container instead of a mount path.
  Binding Block Volumes
  If a user requests a raw block volume by indicating this using the
  volumeMode
  field in the PersistentVolumeClaim spec, the binding rules differ slightly from
  previous releases that didn't consider this mode as part of the spec.
  Listed is a table of possible combinations the user and admin might specify for
  requesting a raw block device. The table indicates if the volume will be bound or
  not given the combinations: Volume binding matrix for statically provisioned volumes:
  PV volumeMode
  PVC volumeMode
  Result
  unspecified
  unspecified
  BIND
  unspecified
  Block
  NO BIND
  unspecified
  Filesystem
  BIND
  Block
  unspecified
  NO BIND
  Block
  Block
  BIND
  Block
  Filesystem
  NO BIND
  Filesystem
  Filesystem
  BIND
  Filesystem
  Block
  NO BIND
  Filesystem
  unspecified
  BIND
  Note:
  Only statically provisioned volumes are supported for alpha release. Administrators
  should take care to consider these values when working with raw block devices.
  Volume Snapshot and Restore Volume from Snapshot Support
  FEATURE STATE:
  Kubernetes v1.20 [stable]
  Volume snapshots only support the out-of-tree CSI volume plugins.
  For details, see
  Volume Snapshots
  In-tree volume plugins are deprecated. You can read about the deprecated volume
  plugins in the
  Volume Plugin FAQ
  Create a PersistentVolumeClaim from a Volume Snapshot
  apiVersion
  kind
  PersistentVolumeClaim
  metadata
  name
  restore-pvc
  spec
  storageClassName
  csi-hostpath-sc
  dataSource
  name
  new-snapshot-test
  kind
  VolumeSnapshot
  apiGroup
  snapshot.storage.k8s.io
  accessModes
  - ReadWriteOnce
  resources
  requests
  storage
  10Gi
  Volume Cloning
  Volume Cloning
  only available for CSI volume plugins.
  Create PersistentVolumeClaim from an existing PVC
  apiVersion
  kind
  PersistentVolumeClaim
  metadata
  name
  cloned-pvc
  spec
  storageClassName
  my-csi-plugin
  dataSource
  name
  existing-src-pvc-name
  kind
  PersistentVolumeClaim
  accessModes
  - ReadWriteOnce
  resources
  requests
  storage
  10Gi
  Volume populators and data sources
  FEATURE STATE:
  Kubernetes v1.24 [beta]
  Kubernetes supports custom volume populators.
  To use custom volume populators, you must enable the
  AnyVolumeDataSource
  feature gate
  the kube-apiserver and kube-controller-manager.
  Volume populators take advantage of a PVC spec field called
  dataSourceRef
  . Unlike the
  dataSource
  field, which can only contain either a reference to another PersistentVolumeClaim
  or to a VolumeSnapshot, the
  dataSourceRef
  field can contain a reference to any object in the
  same namespace, except for core objects other than PVCs. For clusters that have the feature
  gate enabled, use of the
  dataSourceRef
  is preferred over
  dataSource
  Cross namespace data sources
  FEATURE STATE:
  Kubernetes v1.26 [alpha]
  Kubernetes supports cross namespace volume data sources.
  To use cross namespace volume data sources, you must enable the
  AnyVolumeDataSource
  CrossNamespaceVolumeDataSource
  feature gates
  the kube-apiserver and kube-controller-manager.
  Also, you must enable the
  CrossNamespaceVolumeDataSource
  feature gate for the csi-provisioner.
  Enabling the
  CrossNamespaceVolumeDataSource
  feature gate allows you to specify
  a namespace in the dataSourceRef field.
  Note:
  When you specify a namespace for a volume data source, Kubernetes checks for a
  ReferenceGrant in the other namespace before accepting the reference.
  ReferenceGrant is part of the
  gateway.networking.k8s.io
  extension APIs.
  ReferenceGrant
  in the Gateway API documentation for details.
  This means that you must extend your Kubernetes cluster with at least ReferenceGrant from the
  Gateway API before you can use this mechanism.
  Data source references
  dataSourceRef
  field behaves almost the same as the
  dataSource
  field. If one is
  specified while the other is not, the API server will give both fields the same value. Neither
  field can be changed after creation, and attempting to specify different values for the two
  fields will result in a validation error. Therefore the two fields will always have the same
  contents.
  There are two differences between the
  dataSourceRef
  field and the
  dataSource
  field that
  users should be aware of:
  dataSource
  field ignores invalid values (as if the field was blank) while the
  dataSourceRef
  field never ignores values and will cause an error if an invalid value is
  used. Invalid values are any core object (objects with no apiGroup) except for PVCs.
  dataSourceRef
  field may contain different types of objects, while the
  dataSource
  field
  only allows PVCs and VolumeSnapshots.
  When the
  CrossNamespaceVolumeDataSource
  feature is enabled, there are additional differences:
  dataSource
  field only allows local objects, while the
  dataSourceRef
  field allows
  objects in any namespaces.
  When namespace is specified,
  dataSource
  dataSourceRef
  are not synced.
  Users should always use
  dataSourceRef
  on clusters that have the feature gate enabled, and
  fall back to
  dataSource
  on clusters that do not. It is not necessary to look at both fields
  under any circumstance. The duplicated values with slightly different semantics exist only for
  backwards compatibility. In particular, a mixture of older and newer controllers are able to
  interoperate because the fields are the same.
  Using volume populators
  Volume populators are
  controllers
  that can
  create non-empty volumes, where the contents of the volume are determined by a Custom Resource.
  Users create a populated volume by referring to a Custom Resource using the
  dataSourceRef
  field:
  apiVersion
  kind
  PersistentVolumeClaim
  metadata
  name
  populated-pvc
  spec
  dataSourceRef
  name
  example-name
  kind
  ExampleDataSource
  apiGroup
  example.storage.k8s.io
  accessModes
  - ReadWriteOnce
  resources
  requests
  storage
  10Gi
  Because volume populators are external components, attempts to create a PVC that uses one
  can fail if not all the correct components are installed. External controllers should generate
  events on the PVC to provide feedback on the status of the creation, including warnings if
  the PVC cannot be created due to some missing component.
  You can install the alpha
  volume data source validator
  controller into your cluster. That controller generates warning Events on a PVC in the case that no populator
  is registered to handle that kind of data source. When a suitable populator is installed for a PVC, it's the
  responsibility of that populator controller to report Events that relate to volume creation and issues during
  the process.
  Using a cross-namespace volume data source
  FEATURE STATE:
  Kubernetes v1.26 [alpha]
  Create a ReferenceGrant to allow the namespace owner to accept the reference.
  You define a populated volume by specifying a cross namespace volume data source
  using the
  dataSourceRef
  field. You must already have a valid ReferenceGrant
  in the source namespace:
  apiVersion
  gateway.networking.k8s.io/v1beta1
  kind
  ReferenceGrant
  metadata
  name
  allow-ns1-pvc
  namespace
  default
  spec
  from
  group
  kind
  PersistentVolumeClaim
  namespace
  group
  snapshot.storage.k8s.io
  kind
  VolumeSnapshot
  name
  new-snapshot-demo
  apiVersion
  kind
  PersistentVolumeClaim
  metadata
  name
  foo-pvc
  namespace
  spec
  storageClassName
  example
  accessModes
  - ReadWriteOnce
  resources
  requests
  storage
  dataSourceRef
  apiGroup
  snapshot.storage.k8s.io
  kind
  VolumeSnapshot
  name
  new-snapshot-demo
  namespace
  default
  volumeMode
  Filesystem
  Writing Portable Configuration
  If you're writing configuration templates or examples that run on a wide range of clusters
  and need persistent storage, it is recommended that you use the following pattern:
  Include PersistentVolumeClaim objects in your bundle of config (alongside
  Deployments, ConfigMaps, etc).
  Do not include PersistentVolume objects in the config, since the user instantiating
  the config may not have permission to create PersistentVolumes.
  Give the user the option of providing a storage class name when instantiating
  the template.
  If the user provides a storage class name, put that value into the
  persistentVolumeClaim.storageClassName
  field.
  This will cause the PVC to match the right storage
  class if the cluster has StorageClasses enabled by the admin.
  If the user does not provide a storage class name, leave the
  persistentVolumeClaim.storageClassName
  field as nil. This will cause a
  PV to be automatically provisioned for the user with the default StorageClass
  in the cluster. Many cluster environments have a default StorageClass installed,
  or administrators can create their own default StorageClass.
  In your tooling, watch for PVCs that are not getting bound after some time
  and surface this to the user, as this may indicate that the cluster has no
  dynamic storage support (in which case the user should create a matching PV)
  or the cluster has no storage system (in which case the user cannot deploy
  config requiring PVCs).
  What's next
  Learn more about
  Creating a PersistentVolume
  Learn more about
  Creating a PersistentVolumeClaim
  Read the
  Persistent Storage design document
  API references
  Read about the APIs described in this page:
  PersistentVolume
  PersistentVolumeClaim
  Was this page helpful?
  Thanks for the feedback. If you have a specific, answerable question about how to use Kubernetes, ask it on
  Stack Overflow
  Open an issue in the
  GitHub Repository
  if you want to
  report a problem
  suggest an improvement
  Last modified October 18, 2024 at 1:15 AM PST:
  Link to PVC API reference from "Persistent Volumes" concept page (#48391) (6b70c3e234)