```
When the `CSIMigration{provider}` feature flag is enabled for a specific in-tree volume plugin,
the `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](#binding)
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](/docs/concepts/storage/storage-classes/),
access modes, and requested storage size are valid.
```yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: foo-pvc
namespace: foo
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.
```yaml
apiVersion: v1
kind: PersistentVolume
metadata:
name: foo-pv
spec:
storageClassName: ""
claimRef:
name: foo-pvc
namespace: foo
...
```
This is useful if you want to consume PersistentVolumes that have their `persistentVolumeReclaimPolicy` set
to `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:
* csi (including some CSI migrated
volume types)
* flexVolume (deprecated)
* portworxVolume (deprecated)
You can only expand a PVC if its storage class's `allowVolumeExpansion` field is set to true.
```yaml
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.
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.
If 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.
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` and `Block`.
`volumeMode` is an optional API parameter.
`Filesystem` is the default mode used when `volumeMode` parameter is omitted.
A volume with `volumeMode: Filesystem` is *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` to `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.
See [Raw Block Volume Support](#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 (read from or write to) that 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:
The ReadWriteOncePod access mode is only supported for
CSI volumes and Kubernetes version
1.22+. To use this feature you will need to update the following
CSI sidecars
to these versions or greater:
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 not 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 | ✓ | ✓ | ✓ | - |
| CSI | depends on the driver | depends on the driver | depends on the driver | depends on the driver |
| FC | ✓ | ✓ | - | - |
| FlexVolume | ✓ | ✓ | depends on the driver | - |
| HostPath | ✓ | - | - | - |
| iSCSI | ✓ | ✓ | - | - |
| NFS | ✓ | ✓ | ✓ | - |
| RBD | ✓ | ✓ | - | - |
| 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](/docs/concepts/storage/storage-classes/).
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 1.36, only `nfs` and `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:
* `csi` (including CSI migrated volume types)
* `iscsi`
* `nfs`
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.
FEATURE STATE:
Kubernetes v1.35 [alpha](disabled by default)
If the `MutablePVNodeAffinity` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) is enabled in your cluster,
the `.spec.nodeAffinity` field of a PersistentVolume is mutable.
This allows cluster administrators or external storage controller to update the node affinity of a PersistentVolume when the data is migrated,
without interrupting the running pods.
When updating the node affinity, you should ensure that the new node affinity still matches the nodes where the volume is currently in use.
For the pods violating the new affinity, if the pod is already running, it may continue to run. But Kubernetes does not support this configuration.
You should terminate the violating pods soon.
Due to in memory caching, the pods created after the update may still be scheduled according to the old node affinity for a short period of time.
To use this feature, you should enable the `MutablePVNodeAffinity` feature gate on the following components:
- `kube-apiserver`
- `kubelet`
### 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 `.
#### Phase transition timestamp
FEATURE STATE:
Kubernetes v1.31 [stable](enabled by default)
The `.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` and `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](/docs/concepts/overview/working-with-objects/names#dns-subdomain-names).
```yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: myclaim
spec:
accessModes:
- ReadWriteOnce
volumeMode: Filesystem
resources:
requests:
storage: 8Gi
storageClassName: slow
selector:
matchLabels:
release: "stable"
matchExpressions:
- {key: environment, operator: In, values: [dev]}
```
### Access Modes
Claims use [the same conventions as volumes](#access-modes) when requesting
storage with specific access modes.
### Volume Modes
Claims use [the same convention as volumes](#volume-mode) to indicate the
consumption of the volume as either a filesystem or block device.
### Volume Name
Claims can use the `volumeName` field to explicitly bind to a specific PersistentVolume. You can also leave
`volumeName` unset, indicating that you'd like Kubernetes to set up a new PersistentVolume
that matches the claim.
If the specified PV is already bound to another PVC, the binding will be stuck
in a pending state.
### Resources
Claims, like Pods, can request specific quantities of a resource. In this case,
the request is for storage. The same
[resource model](https://git.k8s.io/design-proposals-archive/scheduling/resources.md)
applies to both volumes and claims.
Note:
For Filesystem volumes, the storage request refers to the "outer" volume size
(i.e. the allocated size from the storage backend).
This means that the writeable size may be slightly lower for providers that
build a filesystem on top of a block device, due to filesystem overhead.
This is especially visible with XFS, where many metadata features are enabled by default.
### Selector
Claims can specify a
[label selector](/docs/concepts/overview/working-with-objects/labels/#label-selectors)
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` and `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](/docs/concepts/storage/storage-classes/)
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` set
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](/docs/reference/access-authn-authz/admission-controllers/#defaultstorageclass)
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` in 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 `""`.
See [retroactive default StorageClass assignment](#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
of `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` is `""`, 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.
### Unused PVC tracking
FEATURE STATE:
Kubernetes v1.36 [alpha](disabled by default)
When enabled, the PVC protection controller adds an `Unused`
[condition](/docs/concepts/workloads/pods/pod-lifecycle/#pod-conditions) to each
PersistentVolumeClaim to indicate whether it is currently referenced by any
non-terminal Pod.
The condition has two states:
`Unused` with status `"True"` (reason `NoPodsUsingPVC`)
: No non-terminal Pod references this PVC. The `lastTransitionTime` records when
the PVC became unused.
`Unused` with status `"False"` (reason `PodUsingPVC`)
: At least one non-terminal Pod currently references this PVC. The
`lastTransitionTime` records when the PVC started being used.
A Pod is considered non-terminal if its phase is not `Succeeded` or `Failed`.
This means that a Pending Pod (even one that has not yet been scheduled) counts
as using the PVC.
The `lastTransitionTime` of the `Unused` condition can be used by cluster
administrators, monitoring tools, and external controllers to identify PVCs that
have been unused for a long time. For example, to find all PVCs that have been
unused for more than 30 days, you could query for PVCs where the `Unused`
condition has `status: "True"` and `lastTransitionTime` is older than 30 days.
Note:
The unused duration indicated by this condition may be shorter than the actual
unused time because of processing delays in the controller or because the
feature was enabled after the PVC was already unused. The condition is not
updated when a PVC has deletionTimestamp set (that is, PVCs that are being deleted).
## 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.
```yaml
apiVersion: v1
kind: Pod
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 (`ROX`, `RWX`) is only
possible within one namespace.
### PersistentVolumes typed `hostPath`
A `hostPath` PersistentVolume uses a file or directory on the Node to emulate
network-attached storage. See
[an example of `hostPath` typed volume](/docs/tutorials/configuration/configure-persistent-volume-storage/#create-a-persistentvolume).
## Raw Block Volume Support
FEATURE STATE:
Kubernetes v1.18 [stable]
The following volume plugins support raw block volumes, including dynamic provisioning where
applicable:
* CSI (including some CSI migrated volume types)
* FC (Fibre Channel)
* iSCSI
* Local volume
### PersistentVolume using a Raw Block Volume {#persistent-volume-using-a-raw-block-volume}
```yaml
apiVersion: v1
kind: PersistentVolume
metadata:
name: block-pv
spec:
capacity:
storage: 10Gi
accessModes:
- ReadWriteOnce
volumeMode: Block
persistentVolumeReclaimPolicy: Retain
fc:
targetWWNs: ["50060e801049cfd1"]
lun: 0
readOnly: false
```
### PersistentVolumeClaim requesting a Raw Block Volume {#persistent-volume-claim-requesting-a-raw-block-volume}
```yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: block-pvc
spec:
accessModes:
- ReadWriteOnce
volumeMode: Block
resources:
requests:
storage: 10Gi
```
### Pod specification adding Raw Block Device path in container
```yaml
apiVersion: v1
kind: Pod
metadata:
name: pod-with-block-volume
spec:
containers:
- name: fc-container
image: fedora:26
command: ["/bin/sh", "-c"]
args: [ "tail -f /dev/null" ]
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](/docs/concepts/storage/volume-snapshots/).
In-tree volume plugins are deprecated. You can read about the deprecated volume
plugins in the
[Volume Plugin FAQ](https://github.com/kubernetes/community/blob/main/sig-storage/volume-plugin-faq.md).
### Create a PersistentVolumeClaim from a Volume Snapshot {#create-persistent-volume-claim-from-volume-snapshot}
```yaml
apiVersion: v1
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](/docs/concepts/storage/volume-pvc-datasource/)
only available for CSI volume plugins.
### Create PersistentVolumeClaim from an existing PVC {#create-persistent-volume-claim-from-an-existing-pvc}
```yaml
apiVersion: v1
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
[Volume cloning](#volume-cloning) and
[snapshot restore](#volume-snapshot-and-restore-volume-from-snapshot-support) pre-populate
a new volume from a built-in _data source_. _Volume populators_ extend this mechanism so that
a PersistentVolumeClaim can be pre-populated from other kinds of source (a custom resource),
referenced through its `dataSourceRef` field:
```yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: populated-pvc
spec:
dataSourceRef:
name: example-name
kind: ExampleDataSource
apiGroup: example.storage.k8s.io
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 10Gi
```
For details, including cross-namespace data sources, see
[Volume Populators and Data Sources](/docs/concepts/storage/volume-populators-and-data-sources/).
## 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](/docs/tutorials/configuration/configure-persistent-volume-storage/#create-a-persistentvolume).
* Learn more about [Creating a PersistentVolumeClaim](/docs/tutorials/configuration/configure-persistent-volume-storage/#create-a-persistentvolumeclaim).
* Read the [Persistent Storage design document](https://git.k8s.io/design-proposals-archive/storage/persistent-storage.md).
### API references {#reference}
Read about the APIs described in this page:
* [`PersistentVolume`](/docs/reference/kubernetes-api/config-and-storage-resources/persistent-volume-v1/)
* [`PersistentVolumeClaim`](/docs/reference/kubernetes-api/config-and-storage-resources/persistent-volume-claim-v1/)