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doc: added docs for snapshot-backed CephFS volumes
Signed-off-by: Robert Vasek <robert.vasek@cern.ch>
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docs/cephfs-snapshot-backed-volumes.md
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docs/cephfs-snapshot-backed-volumes.md
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# Provisioning and mounting CephFS snapshot-backed volumes
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Snapshot-backed volumes allow CephFS subvolume snapshots to be exposed as
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regular read-only PVCs. No data cloning is performed and provisioning such
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volumes is done in constant time.
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For more details please refer to [Snapshots as shallow read-only volumes](./design/proposals/cephfs-snapshot-shallow-ro-vol.md)
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design document.
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## Prerequisites
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Prerequisites for this feature are the same as for creating PVCs with snapshot
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volume source. See [Create snapshot and Clone Volume](./snap-clone.md) for more
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information.
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## Usage
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### Provisioning a snapshot-backed volume from a volume snapshot
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For provisioning new snapshot-backed volumes, following configuration must be
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set for storage class(es) and their PVCs respectively:
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* StorageClass:
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* Specify `backingSnapshot: "true"` parameter.
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* PersistentVolumeClaim:
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* Set `storageClassName` to point to your storage class with backing
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snapshots enabled.
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* Define `spec.dataSource` for your desired source volume snapshot.
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* Set `spec.accessModes` to `ReadOnlyMany`. This is the only access mode that
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is supported by this feature.
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### Mounting snapshots from pre-provisioned volumes
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Steps for defining a PersistentVolume and PersistentVolumeClaim for
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pre-provisioned CephFS subvolumes are identical to those described in
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[Static PVC with ceph-csi](./static-pvc.md), except one additional parameter
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must be specified: `backingSnapshotID`. CephFS-CSI driver will retrieve the
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snapshot identified by the given ID from within the specified subvolume, and
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expose it to workloads in read-only mode. Volume access mode must be set to
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`ReadOnlyMany`.
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Note that the snapshot retrieval is done by traversing `<rootPath>/.snap` and
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searching for a directory that contains `backingSnapshotID` value in its name.
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The specified snapshot ID does not necessarily need to be the complete directory
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name inside `<rootPath>/.snap`, however it must be complete enough to uniquely
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identify that directory.
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Example:
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```
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$ ls .snap
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_f279df14-6729-4342-b82f-166f45204233_1099511628283
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_a364870e-6729-4342-b82f-166f45204233_1099635085072
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```
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`f279df14-6729-4342-b82f-166f45204233` would be considered a valid value for
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`backingSnapshotID` volume parameter, whereas `6729-4342-b82f-166f45204233`
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would not, as it would be ambiguous.
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If the given snapshot ID is ambiguous, or no such snapshot is found, mounting
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the PVC will fail with INVALID_ARGUMENT error code.
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@ -81,6 +81,7 @@ you're running it inside a k8s cluster and find the config itself).
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| `pool` | no | Ceph pool into which volume data shall be stored |
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| `volumeNamePrefix` | no | Prefix to use for naming subvolumes (defaults to `csi-vol-`). |
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| `snapshotNamePrefix` | no | Prefix to use for naming snapshots (defaults to `csi-snap-`) |
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| `backingSnapshot` | no | Boolean value. The PVC shall be backed by the CephFS snapshot specified in its data source. `pool` parameter must not be specified. (defaults to `false`) |
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| `kernelMountOptions` | no | Comma separated string of mount options accepted by cephfs kernel mounter, by default no options are passed. Check man mount.ceph for options. |
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| `fuseMountOptions` | no | Comma separated string of mount options accepted by ceph-fuse mounter, by default no options are passed. |
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| `csi.storage.k8s.io/provisioner-secret-name`, `csi.storage.k8s.io/node-stage-secret-name` | for Kubernetes | Name of the Kubernetes Secret object containing Ceph client credentials. Both parameters should have the same value |
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# If omitted, defaults to "csi-vol-".
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# volumeNamePrefix: "foo-bar-"
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# (optional) Boolean value. The PVC shall be backed by the CephFS snapshot
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# specified in its data source. `pool` parameter must not be specified.
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# (defaults to `false`)
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# backingSnapshot: "true"
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reclaimPolicy: Delete
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allowVolumeExpansion: true
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mountOptions:
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