Replicate volumes asynchronously

This page describes how to set up and perform asynchronous replication of Google Distributed Cloud (GDC) air-gapped block storage volumes.

Asynchronous replication is used to replicate data from one GDC zone to another. The replicated data can be used for failover if the source zone data becomes unavailable. Note that once a failover is created, the original volume cannot be replicated to the same destination volume. Instead, a new replication relationship must be created.

Before you begin

To use asynchronous block replication, your Infrastructure Operator (IO) must first set up the storage infrastructure between the two zones in which replication is required. Specifically, they first need to peer the relevant storage clusters from each zone. Next, they need to peer the storage virtual machine associated with the organization in which the block storage is provisioned.

Then, ensure that you have the app-volume-replication-admin-global role to administer the VolumeReplicationRelationship resource. In cases where the global API is unavailable, the volume-replication-admin role can be used to directly modify the zonal VolumeReplicationRelationshipReplica resource.

Set up replication

The VolumeReplicationRelationship Custom Resource (CR) services the asynchronous block replication API. This CR exists in the global management API. To enable replication for a given block device, a VolumeReplicationRelationship CR needs to be created on the global management API:

Replicate PVC API

Note: Project Binding is required. Make sure you have attached your project to each Cluster resource in each participating zone.

kubectl --kubeconfig MANAGEMENT_API_SERVER apply -f - <<EOF
apiVersion: storage.global.gdc.goog/v1
kind: VolumeReplicationRelationship
metadata:
  name: VRR_NAME
  namespace: PROJECT
spec:
  source:
    pvc:
      clusterRef: SOURCE_USER_CLUSTER_NAME
      pvcRef: PVC_NAME
    zoneRef: SOURCE_ZONE_NAME
destination:
    pvc:
      clusterRef: DESTINATION_USER_CLUSTER_NAME
    zoneRef: DESTINATION_ZONE_NAME
EOF

Replace the following:

• MANAGEMENT_API_SERVER: the zonal API server's kubeconfig path.
• VRR_NAME: the name of the VolumeReplicationRelationship resource.
• PROJECT: the namespace of the Project resource.
• SOURCE_USER_CLUSTER_NAME: the name of the source user Cluster resource to be connected.
• PVC_NAME: the name of the PersistentVolumeClaim Resource.
• SOURCE_ZONE_NAME: the name of the source Zone Resource.
• DESTINATION_USER_CLUSTER_NAME: the name of the destination user Cluster resource to be connected.
• DESTINATION_ZONE_NAME: the name of the destination Zone Resource.

This example assumes a project named PROJECT is created in an org named my-org and that a PVC named PVC_NAME has already been provisioned. The SOURCE_USER_CLUSTER_NAME is the name of the source cluster on which the PVC exists and DESTINATION_USER_CLUSTER_NAME is the name of the destination cluster where a new PVC will exist.

The source and destination fields of the specification indicate where the data is being replicated from and to, respectively. In this example, the data is replicated from SOURCE_ZONE_NAME to DESTINATION_ZONE_NAME.

Note: The asynchronous block replication service automatically creates a PVC in the destination zone for writing the replicated data. By default, this PVC has the same name as the source PVC; however, you can use the volumeOverrideName field to specify the name of the created PVC. Until a VolumeReplicationFailover is created, though, the destination PVC remains read-only and is not mountable by any workloads.

Replicate virtual machine disks

VolumeReplicationRelationship also services the asynchronous virtual machine disk (VM disk) replication API. The source disk being replicated is called the primary disk. The destination disk that is being replicated to is called the secondary disk. Starting asynchronous replication on a primary disk automatically creates the secondary disk.

Request permissions and access

To replicate virtual machine disks, you must have the Project VirtualMachine Admin role. Follow the steps to verify that you have the Project VirtualMachine Admin role (project-vm-admin) in the namespace of the project where the VM disk resides.

For virtual machine operations using the gdcloud CLI, request your Project IAM Admin to assign you both the Project VirtualMachine Admin role and the Project Viewer (project-viewer) role.

gdcloud

gdcloud compute disks start-async-replication PRIMARY_DISK_NAME \
  --project PROJECT --zone PRIMARY_ZONE \
  --secondary-disk SECONDARY_DISK_NAME --secondary-zone SECONDARY_ZONE

Replace the following:

Variable	Definition
PRIMARY_DISK_NAME	The name of the source disk being replicated.
PROJECT	The GDC project of the primary disk.
PRIMARY_ZONE	The zone where the primary disk resides.
SECONDARY_DISK_NAME	The name of the destination disk to replicate to.
SECONDARY_ZONE	The zone where the secondary disk must reside.

VM Disk API

Start asynchronous replication

Start asynchronous replication on a VM disk using kubectl.

kubectl --kubeconfig MANAGEMENT_API_SERVER apply -f - <<EOF
apiVersion: storage.global.gdc.goog/v1
kind: VolumeReplicationRelationship
metadata:
  name: VRR_NAME
  namespace: PROJECT
spec:
  destination:
    volumeOverrideName: VIRTUAL_MACHINE_DESTINATION_DISK_NAME
    zoneRef: DESTINATION_ZONE_NAME
  source:
    virtualMachineDisk:
      virtualMachineDiskRef: VIRTUAL_MACHINE_SOURCE_DISK_NAME
    zoneRef: SOURCE_ZONE_NAME
EOF

Replace the following:

• MANAGEMENT_API_SERVER: the zonal API server's kubeconfig path.
• VRR_NAME: the name of the VolumeReplicationRelationship resource.
• PROJECT: the namespace of the Project resource.
• VIRTUAL_MACHINE_DESTINATION_DISK_NAME: the name of the VirtualMachineDisk resource on the destination.
• DESTINATION_ZONE_NAME: the name of the destination Zone Resource.
• VIRTUAL_MACHINE_SOURCE_DISK_NAME: the name of the VirtualMachineDisk resource on the source.
• SOURCE_ZONE_NAME: the name of the source Zone Resource.

This example assumes that a project named PROJECT is created in an org named my-org and that a VirtualMachineDisk named VIRTUAL_MACHINE_SOURCE_DISK_NAME has already been provisioned to the VirtualMachine resource.

The source and destination fields of the specification indicate where the data is being replicated from and to respectively. In this example, the data is replicated from SOURCE_ZONE_NAME to DESTINATION_ZONE_NAME.

Note: The asynchronous block replication service automatically creates a VirtualMachineDisk in the destination zone for writing the replicated data. By default, this VirtualMachineDisk has the same name as the source VirtualMachineDisk; however, you can use the volumeOverrideName field to specify the name of the created VirtualMachineDisk. Until a VolumeReplicationFailover is created, though, the destination VirtualMachineDisk remains read-only and won't be mountable by any workloads.

Verification

Check the status of the replication relationship by retrieving the VolumeReplicationRelationship CR from the global API. Reference the following example. Note that the output has been truncated for simplification:

kubectl --kubeconfig MANAGEMENT_API_SERVER get volumereplicationrelationship VRR_NAME \
        -n PROJECT -o yaml

The output is similar to the following:

PVC API

apiVersion: storage.global.gdc.goog/v1
kind: VolumeReplicationRelationship
metadata:
  name: my-pvc-repl
  namespace: my-project
spec:
  destination:
    pvc:
      clusterRef: my-pvc-cluster
    zoneRef: zone2
  source:
    pvc:
      clusterRef: my-pvc-cluster
      pvcRef: my-block-pvc
    zoneRef: zone1
status:
  zones:
  - name: zone1
    replicaStatus:
      message: SnapMirror relationship has been established. Please check the destination
        zone for relationship state
      replicationID: a096621e-f062-11ef-ad24-00a0b89f23fb
      state: Established
  - name: zone2
    replicaStatus:
      exportedSnapshotName: snapmirror.c34f8845-e8c0-11ef-ad24-00a0b89f23fb_2150007868.2025-02-21_150000
      message: SnapMirror relationship has been successfully established
      replicationID: a096621e-f062-11ef-ad24-00a0b89f23fb
      state: Idle

VM Disk API

apiVersion: storage.global.gdc.goog/v1
kind: VolumeReplicationRelationship
metadata:
  name: my-vmdisk-vrr
  namespace: my-project
spec:
  destination:
    zoneRef: zone2
  source:
    virtualMachineDisk:
      virtualMachineDiskRef: my-vmdisk
    zoneRef: zone1
status:
  zones:
  - name: zone1
    replicaStatus:
      message: SnapMirror relationship has been established. Please check the destination
        zone for relationship state
      replicationID: a096621e-f062-11ef-ad24-00a0b89f23fb
      state: Established
  - name: zone2
    replicaStatus:
      exportedSnapshotName: snapmirror.c34f8845-e8c0-11ef-ad24-00a0b89f23fb_2150007868.2025-02-21_150000
      message: SnapMirror relationship has been successfully established
      replicationID: a096621e-f062-11ef-ad24-00a0b89f23fb
      state: Idle

Create failover

In case the source zone is unavailable for any reason, a VolumeFailover CR can be created in the organization's management plane of the destination zone. For a v2 organization, this would be the management API server. For a v1 organization, this would be the organization admin cluster. For example, if a VolumeReplicationRelationship was created which specifies zone2 as the destination zone and a PVC or VirtualMachineDisk exists in the my-org organization, then the VolumeFailover CR is created in the my-org management plane in zone2. This breaks the replication relationship between the two zones, and allows a workload to mount the PVC or VirtualMachineDisk in the destination zone:

  kubectl --kubeconfig MANAGEMENT_API_SERVER apply -f - <<EOF
  apiVersion: storage.gdc.goog/v1
  kind: VolumeFailover
  metadata:
    name: FAILOVER_NAME
    namespace: PROJECT
  spec:
    volumeReplicationRelationshipRef: VRR_NAME
  EOF

Replace the following:

• FAILOVER_NAME: the name of the VolumeFailover resource.
• MANAGEMENT_API_SERVER: the zonal API server's kubeconfig path.
• VRR_NAME: the name of the VolumeReplicationRelationship resource.
• PROJECT: the namespace of the Project resource.

After, a successful failover is reflected in the status of the CR:

  kubectl --kubeconfig MANAGEMENT_API_SERVER get volumefailover FAILOVER_NAME \
          -n PROJECT -o yaml

• The output is similar to the following:

  apiVersion: storage.gdc.goog/v1
  kind: VolumeFailover
  metadata:
    name: my-failover
    namespace: my-project
  spec:
    volumeReplicationRelationshipRef: my-vrr-repl
  status:
      state: Completed
  

• After the failover is created, the my-vrr-repl VolumeReplicationRelationship transitions to a Broken Off state. The PVC or VirtualMachineDisk in zone2 is now mountable.

• At this point, the VolumeReplicationRelationship will look similar to the following example. Again, this output has been truncated for simplification:

  kubectl --kubeconfig MANAGEMENT_API_SERVER get volumereplicationrelationship VRR_NAME \
          -n PROJECT -o yaml
  

• The output is similar to the following:

PVC API

apiVersion: storage.global.gdc.goog/v1
kind: VolumeReplicationRelationship
metadata:
  name: my-vrr-repl
  namespace: my-project
spec:
  destination:
    pvc:
      clusterRef: my-pvc-cluster
    zoneRef: zone2
  source:
    pvc:
      clusterRef: my-pvc-cluster
      pvcRef: my-block-pvc
    zoneRef: zone1
status:
  zones:
  - name: zone1
    replicaStatus:
      message: SnapMirror relationship has been broken off
      replicationID: a096621e-f062-11ef-ad24-00a0b89f23fb
      state: Broken Off
  - name: zone2
    replicaStatus:
      exportedSnapshotName: snapmirror.c34f8845-e8c0-11ef-ad24-00a0b89f23fb_2150007868.2025-02-21_150000
      message: SnapMirror relationship has been broken off
      replicationID: a096621e-f062-11ef-ad24-00a0b89f23fb
      state: Broken Off

VM Disk API

apiVersion: storage.global.gdc.goog/v1
kind: VolumeReplicationRelationship
metadata:
  name: my-vmdisk-vrr
  namespace: my-project
spec:
  destination:
    zoneRef: zone2
  source:
    virtualMachineDisk:
      virtualMachineDiskRef: my-vmdisk
    zoneRef: zone1
status:
  zones:
  - name: zone1
    replicaStatus:
      message: SnapMirror relationship has been broken off
      replicationID: a096621e-f062-11ef-ad24-00a0b89f23fb
      state: Broken Off
  - name: zone2
    replicaStatus:
      exportedSnapshotName: snapmirror.c34f8845-e8c0-11ef-ad24-00a0b89f23fb_2150007868.2025-02-21_150000
      message: SnapMirror relationship has been broken off
      replicationID: a096621e-f062-11ef-ad24-00a0b89f23fb
      state: Broken Off

• You can now safely delete the VolumeReplicationRelationship because it is the only action remaining that can be done on this CR.

  kubectl --kubeconfig MANAGEMENT_API_SERVER delete volumereplicationrelationship VRR_NAME \
          -n PROJECT
  

Resize volumes

If at any point the source volume is resized, you must also resize the corresponding volume in the destination zone to match. The destination zone volume is created when you create the VolumeReplicationRelationship.

Refer to the Expand VM disks documentation or the Expand volume capacity for resizing storage on both source and destination zones.

List asynchronous replication relationships

List asynchronous replication relationships in a project using kubectl.

kubectl --kubeconfig MANAGEMENT_API_SERVER get volumereplicationrelationships -n PROJECT

Replace the following:

• PROJECT: The GDC project of the primary disk.
• MANAGEMENT_API_SERVER: The kubeconfig file for the zonal management API server.

The output looks similar to the following:

NAME       AGE     SOURCE ZONE   SOURCE PVC   SOURCE PVC CLUSTER   SOURCE VM DISK      DEST. ZONE   DEST. PVC CLUSTER   DEST. VOLUME OVERRIDE     STATE
my-vrr     3m21s   zone1                                           my-vm-boot-disk     zone2                            my-vm-boot-disk-replica
test-vrr   7s      zone1                                           test-vm-boot-disk   zone2

Stop asynchronous replication

Stop asynchronous replication on a primary VM disk using gdcloud or kubectl.

gdcloud

gdcloud compute disks stop-async-replication PRIMARY_DISK_NAME \
  --project PROJECT --zone PRIMARY_ZONE

Replace the following:

Variable	Definition
PRIMARY_DISK_NAME	The name of the source disk being replicated.
PROJECT	The GDC project of the primary disk.
PRIMARY_ZONE	The zone where the primary disk resides.

API

1. Find the volume replication relationships corresponding to the primary VM disk.

   kubectl --kubeconfig MANAGEMENT_API_SERVER get volumereplicationrelationships \
     -n PROJECT -o json | \
     jq -r '.items[] | select(.spec.source.virtualMachineDisk.virtualMachineDiskRef == "PRIMARY_DISK_NAME"
     and .spec.source.zoneRef == "PRIMARY_ZONE") | .metadata.name'
   

2. Delete each of the volume replication relationships listed in the previous step. Replace VRR_NAMES with the names of the volume replication relationships.

   kubectl --kubeconfig MANAGEMENT_API_SERVER delete volumereplicationrelationships \
     -n PROJECT VRR_NAMES
   

   Replace the following:

   Variable	Definition
   MANAGEMENT_API_SERVER	The kubeconfig file for the global management API server.
   PROJECT	The GDC project of the primary disk.
   PRIMARY_DISK_NAME	The name of the source disk being replicated.
   PRIMARY_ZONE	The zone where the primary disk resides.

If the source zone is unavailable for any reason, create a volume failover to stop replication.

Attach the replicated disk to a VM

While replication is enabled, the secondary disk cannot be attached to a VM. After replication is stopped, you can attach the secondary disk to a newly created VM or to an existing VM.