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Migrate Volumes

Volume Migration is an important operation and maintenance management function of HwameiStor. Application-mounted data volumes can be unmounted and migrated from a node with errors or an alert indicating an impending errors to a healthy node. After the data volume is successfully migrated, the Pods of related applications are also rescheduled to the new node and the new data volume is bound and mounted.

Basic concepts​

LocalVolumeGroup(LVG) management is an important function in HwameiStor. When an application Pod applies for multiple data volume PVCs, in order to ensure the correct operation of the Pod, these data volumes must have certain attributes, such as the number of copies of the data volume and the node where the copies are located. Properly managing these associated data volumes through the data volume group management function is a very important capability in HwameiStor.

Prerequisites​

LocalVolumeMigrate needs to be deployed in the Kubernetes system, and the deployed application needs to meet the following conditions:

  • Support lvm type volumes
    • When migrating based on LocalVolume granularity, the data volumes belonging to the same LocalVolumeGroup by default will not be migrated together (if they are migrated together, you need to configure the switch MigrateAllVols: true)

Step 1: Create convertible StorageClass​

$ cd ../../deploy/
$ kubectl apply -f storageclass-convertible-lvm.yaml

Step 2: Create multiple PVCs​

$ kubectl apply -f pvc-multiple-lvm.yaml

Step 3: Deploy multi-volume pod​

$ kubectl apply -f nginx-multiple-lvm.yaml

Step 4: Detach multi-volume pod​

$ kubectl -n hwameistor scale --current-replicas=1 --replicas=0 deployment/nginx-local-storage-lvm

Step 5: Create migration tasks​

$ cat << EOF | kubectl apply -f -
apiVersion: hwameistor.io/v1alpha1
kind: LocalVolumeMigrate
metadata:
  namespace: hwameistor
  name: <localVolumeMigrateName>
  annotations:
    hwameistor.io/replica-affinity: <need/forbid> 
spec:
  sourceNode: <sourceNodeName>
  targetNodesSuggested: 
  - <targetNodesName1>
  - <targetNodesName2>
  volumeName: <volName>
  migrateAllVols: <true/false>
EOF

Attentions:

1) HwameiStor will select a target node from targetNodesSuggested to migrate. If all the candidates don't have enough storage space, the migrate will fail.

2) If targetNodesSuggested is emtpy or not set, HwameiStore will automatically select a propriate node for the migrate. If there is no valid candidate, the migrate will fail.

3) If you do not plan to consider the affinity of the pod during the migration process, just back up the data once. hwameistor.io/replica-affinity: forbid

$ cat << EOF | kubectl apply -f -
apiVersion: hwameistor.io/v1alpha1
kind: LocalVolumeMigrate
metadata:
  namespace: hwameistor
  name: <localVolumeMigrateName>
spec:
  sourceNode: <sourceNodeName>
  targetNodesSuggested: []
  volumeName: <volName>
  migrateAllVols: <true/false>
EOF

Step 6: Check migration Status​

$ kubectl get LocalVolumeMigrate localvolumemigrate-1 -o yaml
apiVersion: hwameistor.io/v1alpha1
kind: LocalVolumeMigrate
metadata:
  generation: 1
  name: localvolumemigrate-1
  namespace: hwameistor
  resourceVersion: "12828637"
  uid: 78af7f1b-d701-4b03-84de-27fafca58764
spec:
  abort: false
  migrateAllVols: true
  sourceNode: k8s-172-30-40-61
  targetNodesSuggested:
  - k8s-172-30-45-223
  volumeName: pvc-1a0913ac-32b9-46fe-8258-39b4e3b696a4
status:
  originalReplicaNumber: 1
  targetNode: k8s-172-30-45-223
  state: Completed
  message:

Step 7: Verify migration results​

$ kubectl get lvr
NAME                                              CAPACITY     NODE                STATE   SYNCED   DEVICE                                                                  AGE
pvc-1a0913ac-32b9-46fe-8258-39b4e3b696a4-9cdkkn   1073741824   k8s-172-30-45-223   Ready   true     /dev/LocalStorage_PoolHDD-HA/pvc-1a0913ac-32b9-46fe-8258-39b4e3b696a4   77s
pvc-d9d3ae9f-64af-44de-baad-4c69b9e0744a-7ppmrx   1073741824   k8s-172-30-45-223   Ready   true     /dev/LocalStorage_PoolHDD-HA/pvc-d9d3ae9f-64af-44de-baad-4c69b9e0744a   77s

Step 8: Reattach/Remount volume​

$ kubectl -n hwameistor scale --current-replicas=0 --replicas=1 deployment/nginx-local-storage-lvm