[zh] localize blog:2018-07-12-resizing-persistent-volumes-using-kubernetes.md
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layout: blog
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title: '使用 Kubernetes 调整 PersistentVolume 的大小'
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date: 2018-07-12
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slug: resize-pv-using-k8s
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---
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<!--
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layout: blog
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title: 'Resizing Persistent Volumes using Kubernetes'
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date: 2018-07-12
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-->
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<!--
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**Author**: Hemant Kumar (Red Hat)
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-->
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**作者**: Hemant Kumar (Red Hat)
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<!--
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**Editor’s note: this post is part of a [series of in-depth articles](https://kubernetes.io/blog/2018/06/27/kubernetes-1.11-release-announcement/) on what’s new in Kubernetes 1.11**
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In Kubernetes v1.11 the persistent volume expansion feature is being promoted to beta. This feature allows users to easily resize an existing volume by editing the `PersistentVolumeClaim` (PVC) object. Users no longer have to manually interact with the storage backend or delete and recreate PV and PVC objects to increase the size of a volume. Shrinking persistent volumes is not supported.
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Volume expansion was introduced in v1.8 as an Alpha feature, and versions prior to v1.11 required enabling the feature gate, `ExpandPersistentVolumes`, as well as the admission controller, `PersistentVolumeClaimResize` (which prevents expansion of PVCs whose underlying storage provider does not support resizing). In Kubernetes v1.11+, both the feature gate and admission controller are enabled by default.
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Although the feature is enabled by default, a cluster admin must opt-in to allow users to resize their volumes. Kubernetes v1.11 ships with volume expansion support for the following in-tree volume plugins: AWS-EBS, GCE-PD, Azure Disk, Azure File, Glusterfs, Cinder, Portworx, and Ceph RBD. Once the admin has determined that volume expansion is supported for the underlying provider, they can make the feature available to users by setting the `allowVolumeExpansion` field to `true` in their `StorageClass` object(s). Only PVCs created from that `StorageClass` will be allowed to trigger volume expansion.
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-->
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**编者注：这篇博客是[深度文章系列](https://kubernetes.io/blog/2018/06/27/kubernetes-1.11-release-announcement/)的一部分，这个系列介绍了 Kubernetes 1.11 中的新增特性**
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在 Kubernetes v1.11 中，持久化卷扩展功能升级为 Beta。
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该功能允许用户通过编辑 `PersistentVolumeClaim`（PVC）对象，轻松调整已存在数据卷的大小。
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用户不再需要手动与存储后端交互，或者删除再重建 PV 和 PVC 对象来增加卷的大小。缩减持久化卷暂不支持。
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卷扩展是在 v1.8 版本中作为 Alpha 功能引入的，
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在 v1.11 之前的版本都需要开启特性门控 `ExpandPersistentVolumes` 以及准入控制器 `PersistentVolumeClaimResize`（防止扩展底层存储供应商不支持调整大小的 PVC）。
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在 Kubernetes v1.11+ 中，特性门控和准入控制器都是默认启用的。
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虽然该功能默认是启用的，但集群管理员必须选择允许用户调整数据卷的大小。
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Kubernetes v1.11 为以下树内卷插件提供了卷扩展支持：
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AWS-EBS、GCE-PD、Azure Disk、Azure File、Glusterfs、Cinder、Portworx 和 Ceph RBD。
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一旦管理员确定底层供应商支持卷扩展，
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就可以通过在 `StorageClass` 对象中设置 `allowVolumeExpansion` 字段为 `true`，让用户可以使用该功能。
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只有由这个 `StorageClass` 创建的 PVC 才能触发卷扩展。
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```
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~> cat standard.yaml
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apiVersion: storage.k8s.io/v1
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kind: StorageClass
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metadata:
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name: standard
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parameters:
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type: pd-standard
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provisioner: kubernetes.io/gce-pd
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allowVolumeExpansion: true
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reclaimPolicy: Delete
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```
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<!--
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Any PVC created from this `StorageClass` can be edited (as illustrated below) to request more space. Kubernetes will interpret a change to the storage field as a request for more space, and will trigger automatic volume resizing.
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-->
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从这个 `StorageClass` 创建的任何 PVC 都可以被编辑（如下图所示）以请求更多的空间。
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Kubernetes 会将存储字段的变化解释为对更多空间的请求，并触发卷大小的自动调整。
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<!--
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## File System Expansion
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Block storage volume types such as GCE-PD, AWS-EBS, Azure Disk, Cinder, and Ceph RBD typically require a file system expansion before the additional space of an expanded volume is usable by pods. Kubernetes takes care of this automatically whenever the pod(s) referencing your volume are restarted.
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Network attached file systems (like Glusterfs and Azure File) can be expanded without having to restart the referencing Pod, because these systems do not require special file system expansion.
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File system expansion must be triggered by terminating the pod using the volume. More specifically:
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* Edit the PVC to request more space.
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* Once underlying volume has been expanded by the storage provider, then the PersistentVolume object will reflect the updated size and the PVC will have the `FileSystemResizePending` condition.
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You can verify this by running `kubectl get pvc <pvc_name> -o yaml`
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-->
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## 文件系统扩展 {#file-system-expansion}
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如 GCE-PD、AWS-EBS、Azure Disk、Cinder 和 Ceph RBD 这类的块存储卷类型，
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通常需要在扩展卷的额外空间被 Pod 使用之前进行文件系统扩展。
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Kubernetes 会在引用数据卷的 Pod 重新启动时自动处理这个问题。
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网络附加文件系统（如 Glusterfs 和 Azure File）可以被扩展，而不需要重新启动引用的 Pod，
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因为这些系统不需要特殊的文件系统扩展。
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文件系统扩展必须通过终止使用该卷的 Pod 来触发。更具体地说：
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* 编辑 PVC 以请求更多的空间。
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* 一旦底层卷被存储提供商扩展后， PersistentVolume 对象将反映更新的大小，PVC 会有 `FileSystemResizePending` 状态。
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你可以通过运行 `kubectl get pvc <pvc_name> -o yaml` 来验证这一点。
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```
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~> kubectl get pvc myclaim -o yaml
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apiVersion: v1
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kind: PersistentVolumeClaim
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metadata:
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name: myclaim
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namespace: default
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uid: 02d4aa83-83cd-11e8-909d-42010af00004
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spec:
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accessModes:
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- ReadWriteOnce
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resources:
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requests:
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storage: 14Gi
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storageClassName: standard
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volumeName: pvc-xxx
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status:
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capacity:
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storage: 9G
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conditions:
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- lastProbeTime: null
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lastTransitionTime: 2018-07-11T14:51:10Z
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message: Waiting for user to (re-)start a pod to finish file system resize of
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volume on node.
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status: "True"
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type: FileSystemResizePending
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phase: Bound
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```
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<!--
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* Once the PVC has the condition `FileSystemResizePending` then pod that uses the PVC can be restarted to finish file system resizing on the node. Restart can be achieved by deleting and recreating the pod or by scaling down the deployment and then scaling it up again.
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* Once file system resizing is done, the PVC will automatically be updated to reflect new size.
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Any errors encountered while expanding file system should be available as events on pod.
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-->
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* 一旦 PVC 具有 `FileSystemResizePending` 状态 ，就可以重启使用该 PVC 的 Pod 以完成节点上的文件系统大小调整。
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重新启动可以通过删除并重新创建 Pod，或者通过 Deployment 缩容后再扩容来实现。
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* 一旦文件系统的大小调整完成，PVC 将自动更新以展现新的大小。
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在扩展文件系统时遇到的任何错误都应作为 Pod 的事件而存在。
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<!--
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## Online File System Expansion
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Kubernetes v1.11 also introduces an alpha feature called online file system expansion. This feature enables file system expansion while a volume is still in-use by a pod. Because this feature is alpha, it requires enabling the feature gate, `ExpandInUsePersistentVolumes`. It is supported by the in-tree volume plugins GCE-PD, AWS-EBS, Cinder, and Ceph RBD. When this feature is enabled, pod referencing the resized volume do not need to be restarted. Instead, the file system will automatically be resized while in use as part of volume expansion. File system expansion does not happen until a pod references the resized volume, so if no pods referencing the volume are running file system expansion will not happen.
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-->
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## 在线文件系统扩展 {#online-file-system-expansion}
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Kubernetes v1.11 里还引入了一个名为在线文件系统扩展的 Alpha 功能。
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该功能可以让一个正在被 Pod 使用的卷进行文件系统扩展。
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因为这个功能是 Alpha 阶段，所以它需要启用特性门控 `ExpandInUsePersistentVolumes`。
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树内卷插件 GCE-PD、AWS-EBS、Cinder 和 Ceph RBD 都支持该功能。
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当这个功能被启用时，引用调整后的卷的 Pod 不需要被重新启动。
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相反，在使用中文件系统将作为卷扩展的一部分自动调整大小。
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文件系统的扩展是在一个 Pod 引用调整后的卷时才发生的，所以如果没有引用卷的 Pod 在运行，文件系统的扩展就不会发生。
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<!--
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## How can I learn more?
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Check out additional documentation on this feature here: http://k8s.io/docs/concepts/storage/persistent-volumes.
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-->
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## 更多信息 {#how-can-i-learn-more}
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在这里查看有关这一特性的其他文档：
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https://kubernetes.io/zh-cn/docs/concepts/storage/persistent-volumes/
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