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Storage Classes

This document describes the concept of a StorageClass in Kubernetes. Familiarity with volumes and persistent volumes is suggested.

• Introduction
• The StorageClass Resource
• Parameters

Introduction

A StorageClass provides a way for administrators to describe the “classes” of storage they offer. Different classes might map to quality-of-service levels, or to backup policies, or to arbitrary policies determined by the cluster administrators. Kubernetes itself is unopinionated about what classes represent. This concept is sometimes called “profiles” in other storage systems.

The StorageClass Resource

Each StorageClass contains the fields provisioner, parameters, and reclaimPolicy, which are used when a PersistentVolume belonging to the class needs to be dynamically provisioned.

The name of a StorageClass object is significant, and is how users can request a particular class. Administrators set the name and other parameters of a class when first creating StorageClass objects, and the objects cannot be updated once they are created.

Administrators can specify a default StorageClass just for PVCs that don’t request any particular class to bind to: see the PersistentVolumeClaim section for details.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: standard
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp2
reclaimPolicy: Retain
allowVolumeExpansion: true
mountOptions:
  - debug
volumeBindingMode: Immediate

Provisioner

Storage classes have a provisioner that determines what volume plugin is used for provisioning PVs. This field must be specified.

You are not restricted to specifying the “internal” provisioners listed here (whose names are prefixed with “kubernetes.io” and shipped alongside Kubernetes). You can also run and specify external provisioners, which are independent programs that follow a specification defined by Kubernetes. Authors of external provisioners have full discretion over where their code lives, how the provisioner is shipped, how it needs to be run, what volume plugin it uses (including Flex), etc. The repository kubernetes-sigs/sig-storage-lib-external-provisioner houses a library for writing external provisioners that implements the bulk of the specification. Some external provisioners are listed under the repository kubernetes-incubator/external-storage.

For example, NFS doesn’t provide an internal provisioner, but an external provisioner can be used. There are also cases when 3rd party storage vendors provide their own external provisioner.

Reclaim Policy

Persistent Volumes that are dynamically created by a storage class will have the reclaim policy specified in the reclaimPolicy field of the class, which can be either Delete or Retain. If no reclaimPolicy is specified when a StorageClass object is created, it will default to Delete.

Persistent Volumes that are created manually and managed via a storage class will have whatever reclaim policy they were assigned at creation.

Allow Volume Expansion

Persistent Volumes can be configured to be expandable. This feature when set to true, allows the users to resize the volume by editing the corresponding PVC object.

The following types of volumes support volume expansion, when the underlying Storage Class has the field allowVolumeExpansion set to true.

Note: You can only use the volume expansion feature to grow a Volume, not to shrink it.

Mount Options

Persistent Volumes that are dynamically created by a storage class will have the mount options specified in the mountOptions field of the class.

If the volume plugin does not support mount options but mount options are specified, provisioning will fail. Mount options are not validated on either the class or PV, so mount of the PV will simply fail if one is invalid.

Volume Binding Mode

The volumeBindingMode field controls when volume binding and dynamic provisioning should occur.

By default, the Immediate mode indicates that volume binding and dynamic provisioning occurs once the PersistentVolumeClaim is created. For storage backends that are topology-constrained and not globally accessible from all Nodes in the cluster, PersistentVolumes will be bound or provisioned without knowledge of the Pod’s scheduling requirements. This may result in unschedulable Pods.

A cluster administrator can address this issue by specifying the WaitForFirstConsumer mode which will delay the binding and provisioning of a PersistentVolume until a Pod using the PersistentVolumeClaim is created. PersistentVolumes will be selected or provisioned conforming to the topology that is specified by the Pod’s scheduling constraints. These include, but are not limited to, resource requirements, node selectors, pod affinity and anti-affinity, and taints and tolerations.

The following plugins support WaitForFirstConsumer with dynamic provisioning:

• AWSElasticBlockStore
• GCEPersistentDisk
• AzureDisk

The following plugins support WaitForFirstConsumer with pre-created PersistentVolume binding:

• All of the above
• Local

CSI volumes are also supported with dynamic provisioning and pre-created PVs, but you’ll need to look at the documentation for a specific CSI driver to see its supported topology keys and examples.

Allowed Topologies

When a cluster operator specifies the WaitForFirstConsumer volume binding mode, it is no longer necessary to restrict provisioning to specific topologies in most situations. However, if still required, allowedTopologies can be specified.

This example demonstrates how to restrict the topology of provisioned volumes to specific zones and should be used as a replacement for the zone and zones parameters for the supported plugins.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: standard
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-standard
volumeBindingMode: WaitForFirstConsumer
allowedTopologies:
- matchLabelExpressions:
  - key: failure-domain.beta.kubernetes.io/zone
    values:
    - us-central1-a
    - us-central1-b

Parameters

Storage classes have parameters that describe volumes belonging to the storage class. Different parameters may be accepted depending on the provisioner. For example, the value io1, for the parameter type, and the parameter iopsPerGB are specific to EBS. When a parameter is omitted, some default is used.

There can be at most 512 parameters defined for a StorageClass. The total length of the parameters object including its keys and values cannot exceed 256 KiB.

AWS EBS

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: slow
provisioner: kubernetes.io/aws-ebs
parameters:
  type: io1
  iopsPerGB: "10"
  fsType: ext4

• type: io1, gp2, sc1, st1. See AWS docs for details. Default: gp2.
• zone (Deprecated): AWS zone. If neither zone nor zones is specified, volumes are generally round-robin-ed across all active zones where Kubernetes cluster has a node. zone and zones parameters must not be used at the same time.
• zones (Deprecated): A comma separated list of AWS zone(s). If neither zone nor zones is specified, volumes are generally round-robin-ed across all active zones where Kubernetes cluster has a node. zone and zones parameters must not be used at the same time.
• iopsPerGB: only for io1 volumes. I/O operations per second per GiB. AWS volume plugin multiplies this with size of requested volume to compute IOPS of the volume and caps it at 20 000 IOPS (maximum supported by AWS, see AWS docs. A string is expected here, i.e. "10", not 10.
• fsType: fsType that is supported by kubernetes. Default: "ext4".
• encrypted: denotes whether the EBS volume should be encrypted or not. Valid values are "true" or "false". A string is expected here, i.e. "true", not true.
• kmsKeyId: optional. The full Amazon Resource Name of the key to use when encrypting the volume. If none is supplied but encrypted is true, a key is generated by AWS. See AWS docs for valid ARN value.

Note: zone and zones parameters are deprecated and replaced with allowedTopologies

GCE PD

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: slow
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-standard
  replication-type: none

• type: pd-standard or pd-ssd. Default: pd-standard
• zone (Deprecated): GCE zone. If neither zone nor zones is specified, volumes are generally round-robin-ed across all active zones where Kubernetes cluster has a node. zone and zones parameters must not be used at the same time.
• zones (Deprecated): A comma separated list of GCE zone(s). If neither zone nor zones is specified, volumes are generally round-robin-ed across all active zones where Kubernetes cluster has a node. zone and zones parameters must not be used at the same time.
• replication-type: none or regional-pd. Default: none.

If replication-type is set to none, a regular (zonal) PD will be provisioned.

If replication-type is set to regional-pd, a Regional Persistent Disk will be provisioned. In this case, users must use zones instead of zone to specify the desired replication zones. If exactly two zones are specified, the Regional PD will be provisioned in those zones. If more than two zones are specified, Kubernetes will arbitrarily choose among the specified zones. If the zones parameter is omitted, Kubernetes will arbitrarily choose among zones managed by the cluster.

Note: zone and zones parameters are deprecated and replaced with allowedTopologies

Glusterfs

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: slow
provisioner: kubernetes.io/glusterfs
parameters:
  resturl: "http://127.0.0.1:8081"
  clusterid: "630372ccdc720a92c681fb928f27b53f"
  restauthenabled: "true"
  restuser: "admin"
  secretNamespace: "default"
  secretName: "heketi-secret"
  gidMin: "40000"
  gidMax: "50000"
  volumetype: "replicate:3"

• resturl: Gluster REST service/Heketi service url which provision gluster volumes on demand. The general format should be IPaddress:Port and this is a mandatory parameter for GlusterFS dynamic provisioner. If Heketi service is exposed as a routable service in openshift/kubernetes setup, this can have a format similar to http://heketi-storage-project.cloudapps.mystorage.com where the fqdn is a resolvable Heketi service url.
• restauthenabled : Gluster REST service authentication boolean that enables authentication to the REST server. If this value is "true", restuser and restuserkey or secretNamespace + secretName have to be filled. This option is deprecated, authentication is enabled when any of restuser, restuserkey, secretName or secretNamespace is specified.
• restuser : Gluster REST service/Heketi user who has access to create volumes in the Gluster Trusted Pool.
• restuserkey : Gluster REST service/Heketi user’s password which will be used for authentication to the REST server. This parameter is deprecated in favor of secretNamespace + secretName.

• secretNamespace, secretName : Identification of Secret instance that contains user password to use when talking to Gluster REST service. These parameters are optional, empty password will be used when both secretNamespace and secretName are omitted. The provided secret must have type "kubernetes.io/glusterfs", for example created in this way:

  kubectl create secret generic heketi-secret \
    --type="kubernetes.io/glusterfs" --from-literal=key='opensesame' \
    --namespace=default
  

  Example of a secret can be found in glusterfs-provisioning-secret.yaml.

• clusterid: 630372ccdc720a92c681fb928f27b53f is the ID of the cluster which will be used by Heketi when provisioning the volume. It can also be a list of clusterids, for example: "8452344e2becec931ece4e33c4674e4e,42982310de6c63381718ccfa6d8cf397". This is an optional parameter.

• gidMin, gidMax : The minimum and maximum value of GID range for the storage class. A unique value (GID) in this range ( gidMin-gidMax ) will be used for dynamically provisioned volumes. These are optional values. If not specified, the volume will be provisioned with a value between 2000-2147483647 which are defaults for gidMin and gidMax respectively.

• volumetype : The volume type and its parameters can be configured with this optional value. If the volume type is not mentioned, it’s up to the provisioner to decide the volume type.

  For example:

  • Replica volume: volumetype: replicate:3 where ‘3’ is replica count.
  • Disperse/EC volume: volumetype: disperse:4:2 where ‘4’ is data and ‘2’ is the redundancy count.
  • Distribute volume: volumetype: none

  For available volume types and administration options, refer to the Administration Guide.

  For further reference information, see How to configure Heketi.

  When persistent volumes are dynamically provisioned, the Gluster plugin automatically creates an endpoint and a headless service in the name gluster-dynamic-<claimname>. The dynamic endpoint and service are automatically deleted when the persistent volume claim is deleted.

OpenStack Cinder

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: gold
provisioner: kubernetes.io/cinder
parameters:
  availability: nova

• availability: Availability Zone. If not specified, volumes are generally round-robin-ed across all active zones where Kubernetes cluster has a node.

Note:

FEATURE STATE: Kubernetes 1.11 deprecated

This feature is deprecated. For more information on this state, see the Kubernetes Deprecation Policy.

This internal provisioner of OpenStack is deprecated. Please use the external cloud provider for OpenStack.

vSphere

1. Create a StorageClass with a user specified disk format.

   apiVersion: storage.k8s.io/v1
   kind: StorageClass
   metadata:
     name: fast
   provisioner: kubernetes.io/vsphere-volume
   parameters:
     diskformat: zeroedthick

   diskformat: thin, zeroedthick and eagerzeroedthick. Default: "thin".

2. Create a StorageClass with a disk format on a user specified datastore.

   apiVersion: storage.k8s.io/v1
   kind: StorageClass
   metadata:
     name: fast
   provisioner: kubernetes.io/vsphere-volume
   parameters:
       diskformat: zeroedthick
       datastore: VSANDatastore

   datastore: The user can also specify the datastore in the StorageClass. The volume will be created on the datastore specified in the storage class, which in this case is VSANDatastore. This field is optional. If the datastore is not specified, then the volume will be created on the datastore specified in the vSphere config file used to initialize the vSphere Cloud Provider.

3. Storage Policy Management inside kubernetes

   • Using existing vCenter SPBM policy

     One of the most important features of vSphere for Storage Management is policy based Management. Storage Policy Based Management (SPBM) is a storage policy framework that provides a single unified control plane across a broad range of data services and storage solutions. SPBM enables vSphere administrators to overcome upfront storage provisioning challenges, such as capacity planning, differentiated service levels and managing capacity headroom.

     The SPBM policies can be specified in the StorageClass using the storagePolicyName parameter.

   • Virtual SAN policy support inside Kubernetes

     Vsphere Infrastructure (VI) Admins will have the ability to specify custom Virtual SAN Storage Capabilities during dynamic volume provisioning. You can now define storage requirements, such as performance and availability, in the form of storage capabilities during dynamic volume provisioning. The storage capability requirements are converted into a Virtual SAN policy which are then pushed down to the Virtual SAN layer when a persistent volume (virtual disk) is being created. The virtual disk is distributed across the Virtual SAN datastore to meet the requirements.

     You can see Storage Policy Based Management for dynamic provisioning of volumes for more details on how to use storage policies for persistent volumes management.

There are few vSphere examples which you try out for persistent volume management inside Kubernetes for vSphere.

Ceph RBD

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast
provisioner: kubernetes.io/rbd
parameters:
  monitors: 10.16.153.105:6789
  adminId: kube
  adminSecretName: ceph-secret
  adminSecretNamespace: kube-system
  pool: kube
  userId: kube
  userSecretName: ceph-secret-user
  userSecretNamespace: default
  fsType: ext4
  imageFormat: "2"
  imageFeatures: "layering"

• monitors: Ceph monitors, comma delimited. This parameter is required.
• adminId: Ceph client ID that is capable of creating images in the pool. Default is “admin”.
• adminSecretName: Secret Name for adminId. This parameter is required. The provided secret must have type “kubernetes.io/rbd”.
• adminSecretNamespace: The namespace for adminSecretName. Default is “default”.
• pool: Ceph RBD pool. Default is “rbd”.
• userId: Ceph client ID that is used to map the RBD image. Default is the same as adminId.

• userSecretName: The name of Ceph Secret for userId to map RBD image. It must exist in the same namespace as PVCs. This parameter is required. The provided secret must have type “kubernetes.io/rbd”, for example created in this way:

  kubectl create secret generic ceph-secret --type="kubernetes.io/rbd" \
    --from-literal=key='QVFEQ1pMdFhPUnQrSmhBQUFYaERWNHJsZ3BsMmNjcDR6RFZST0E9PQ==' \
    --namespace=kube-system

• userSecretNamespace: The namespace for userSecretName.

• fsType: fsType that is supported by kubernetes. Default: "ext4".

• imageFormat: Ceph RBD image format, “1” or “2”. Default is “2”.

• imageFeatures: This parameter is optional and should only be used if you set imageFormat to “2”. Currently supported features are layering only. Default is “”, and no features are turned on.

Quobyte

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
   name: slow
provisioner: kubernetes.io/quobyte
parameters:
    quobyteAPIServer: "http://138.68.74.142:7860"
    registry: "138.68.74.142:7861"
    adminSecretName: "quobyte-admin-secret"
    adminSecretNamespace: "kube-system"
    user: "root"
    group: "root"
    quobyteConfig: "BASE"
    quobyteTenant: "DEFAULT"

• quobyteAPIServer: API Server of Quobyte in the format "http(s)://api-server:7860"
• registry: Quobyte registry to use to mount the volume. You can specify the registry as <host>:<port> pair or if you want to specify multiple registries you just have to put a comma between them e.q. <host1>:<port>,<host2>:<port>,<host3>:<port>. The host can be an IP address or if you have a working DNS you can also provide the DNS names.
• adminSecretNamespace: The namespace for adminSecretName. Default is “default”.

• adminSecretName: secret that holds information about the Quobyte user and the password to authenticate against the API server. The provided secret must have type “kubernetes.io/quobyte” and the keys user and password, for example:

  kubectl create secret generic quobyte-admin-secret \
    --type="kubernetes.io/quobyte" --from-literal=user='admin' --from-literal=password='opensesame' \
    --namespace=kube-system

• user: maps all access to this user. Default is “root”.

• group: maps all access to this group. Default is “nfsnobody”.

• quobyteConfig: use the specified configuration to create the volume. You can create a new configuration or modify an existing one with the Web console or the quobyte CLI. Default is “BASE”.

• quobyteTenant: use the specified tenant ID to create/delete the volume. This Quobyte tenant has to be already present in Quobyte. Default is “DEFAULT”.

Azure Disk

Azure Unmanaged Disk Storage Class

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: slow
provisioner: kubernetes.io/azure-disk
parameters:
  skuName: Standard_LRS
  location: eastus
  storageAccount: azure_storage_account_name

• skuName: Azure storage account Sku tier. Default is empty.
• location: Azure storage account location. Default is empty.
• storageAccount: Azure storage account name. If a storage account is provided, it must reside in the same resource group as the cluster, and location is ignored. If a storage account is not provided, a new storage account will be created in the same resource group as the cluster.

New Azure Disk Storage Class (starting from v1.7.2)

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: slow
provisioner: kubernetes.io/azure-disk
parameters:
  storageaccounttype: Standard_LRS
  kind: Shared

• storageaccounttype: Azure storage account Sku tier. Default is empty.
• kind: Possible values are shared (default), dedicated, and managed. When kind is shared, all unmanaged disks are created in a few shared storage accounts in the same resource group as the cluster. When kind is dedicated, a new dedicated storage account will be created for the new unmanaged disk in the same resource group as the cluster. When kind is managed, all managed disks are created in the same resource group as the cluster.

• resourceGroup: Specify the resource group in which the Azure disk will be created. It must be an existing resource group name. If it is unspecified, the disk will be placed in the same resource group as the current Kubernetes cluster.

• Premium VM can attach both Standard_LRS and Premium_LRS disks, while Standard VM can only attach Standard_LRS disks.

• Managed VM can only attach managed disks and unmanaged VM can only attach unmanaged disks.

Azure File

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: azurefile
provisioner: kubernetes.io/azure-file
parameters:
  skuName: Standard_LRS
  location: eastus
  storageAccount: azure_storage_account_name

• skuName: Azure storage account Sku tier. Default is empty.
• location: Azure storage account location. Default is empty.
• storageAccount: Azure storage account name. Default is empty. If a storage account is not provided, all storage accounts associated with the resource group are searched to find one that matches skuName and location. If a storage account is provided, it must reside in the same resource group as the cluster, and skuName and location are ignored.
• secretNamespace: the namespace of the secret that contains the Azure Storage Account Name and Key. Default is the same as the Pod.
• secretName: the name of the secret that contains the Azure Storage Account Name and Key. Default is azure-storage-account-<accountName>-secret
• readOnly: a flag indicating whether the storage will be mounted as read only. Defaults to false which means a read/write mount. This setting will impact the ReadOnly setting in VolumeMounts as well.

During storage provisioning, a secret named by secretName is created for the mounting credentials. If the cluster has enabled both RBAC and Controller Roles, add the create permission of resource secret for clusterrole system:controller:persistent-volume-binder.

In a multi-tenancy context, it is strongly recommended to set the value for secretNamespace explicitly, otherwise the storage account credentials may be read by other users.

Portworx Volume

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: portworx-io-priority-high
provisioner: kubernetes.io/portworx-volume
parameters:
  repl: "1"
  snap_interval:   "70"
  io_priority:  "high"

• fs: filesystem to be laid out: none/xfs/ext4 (default: ext4).
• block_size: block size in Kbytes (default: 32).
• repl: number of synchronous replicas to be provided in the form of replication factor 1..3 (default: 1) A string is expected here i.e. "1" and not 1.
• io_priority: determines whether the volume will be created from higher performance or a lower priority storage high/medium/low (default: low).
• snap_interval: clock/time interval in minutes for when to trigger snapshots. Snapshots are incremental based on difference with the prior snapshot, 0 disables snaps (default: 0). A string is expected here i.e. "70" and not 70.
• aggregation_level: specifies the number of chunks the volume would be distributed into, 0 indicates a non-aggregated volume (default: 0). A string is expected here i.e. "0" and not 0
• ephemeral: specifies whether the volume should be cleaned-up after unmount or should be persistent. emptyDir use case can set this value to true and persistent volumes use case such as for databases like Cassandra should set to false, true/false (default false). A string is expected here i.e. "true" and not true.

ScaleIO

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: slow
provisioner: kubernetes.io/scaleio
parameters:
  gateway: https://192.168.99.200:443/api
  system: scaleio
  protectionDomain: pd0
  storagePool: sp1
  storageMode: ThinProvisioned
  secretRef: sio-secret
  readOnly: false
  fsType: xfs

• provisioner: attribute is set to kubernetes.io/scaleio
• gateway: address to a ScaleIO API gateway (required)
• system: the name of the ScaleIO system (required)
• protectionDomain: the name of the ScaleIO protection domain (required)
• storagePool: the name of the volume storage pool (required)
• storageMode: the storage provision mode: ThinProvisioned (default) or ThickProvisioned
• secretRef: reference to a configured Secret object (required)
• readOnly: specifies the access mode to the mounted volume (default false)
• fsType: the file system to use for the volume (default ext4)

The ScaleIO Kubernetes volume plugin requires a configured Secret object. The secret must be created with type kubernetes.io/scaleio and use the same namespace value as that of the PVC where it is referenced as shown in the following command:

kubectl create secret generic sio-secret --type="kubernetes.io/scaleio" \
--from-literal=username=sioadmin --from-literal=password=d2NABDNjMA== \
--namespace=default

StorageOS

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast
provisioner: kubernetes.io/storageos
parameters:
  pool: default
  description: Kubernetes volume
  fsType: ext4
  adminSecretNamespace: default
  adminSecretName: storageos-secret

• pool: The name of the StorageOS distributed capacity pool to provision the volume from. Uses the default pool which is normally present if not specified.
• description: The description to assign to volumes that were created dynamically. All volume descriptions will be the same for the storage class, but different storage classes can be used to allow descriptions for different use cases. Defaults to Kubernetes volume.
• fsType: The default filesystem type to request. Note that user-defined rules within StorageOS may override this value. Defaults to ext4.
• adminSecretNamespace: The namespace where the API configuration secret is located. Required if adminSecretName set.
• adminSecretName: The name of the secret to use for obtaining the StorageOS API credentials. If not specified, default values will be attempted.

The StorageOS Kubernetes volume plugin can use a Secret object to specify an endpoint and credentials to access the StorageOS API. This is only required when the defaults have been changed. The secret must be created with type kubernetes.io/storageos as shown in the following command:

kubectl create secret generic storageos-secret \
--type="kubernetes.io/storageos" \
--from-literal=apiAddress=tcp://localhost:5705 \
--from-literal=apiUsername=storageos \
--from-literal=apiPassword=storageos \
--namespace=default

Secrets used for dynamically provisioned volumes may be created in any namespace and referenced with the adminSecretNamespace parameter. Secrets used by pre-provisioned volumes must be created in the same namespace as the PVC that references it.

Local

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer

Local volumes do not currently support dynamic provisioning, however a StorageClass should still be created to delay volume binding until pod scheduling. This is specified by the WaitForFirstConsumer volume binding mode.

Delaying volume binding allows the scheduler to consider all of a pod’s scheduling constraints when choosing an appropriate PersistentVolume for a PersistentVolumeClaim.

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