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Simplifying disaster recovery with Trident SnapMirror volume replication for NVMe/TCP

DhruvKharkwal

In today's fast-paced digital world, keeping your data safe and always available is more critical than ever. As enterprises increasingly depend on Kubernetes to deploy and manage their applications, having a robust disaster recovery plan is essential. Enter NetApp^® Trident™ with asynchronous SnapMirror^® volume replication to keep your data secure and your mind at ease.

With the release of v25.06, Trident now supports NVMe/TCP back ends for volume replication using SnapMirror, offering faster and more efficient data transfer capabilities. This blog takes you through the exciting journey of setting up asynchronous SnapMirror volume replication using Trident. So buckle up and let’s dive in! 🌊

Why SnapMirror volume replication?

NetApp SnapMirror technology is a game changer for disaster recovery, enabling efficient data replication between NetApp ONTAP^® clusters. With Trident, you can establish mirror relationships between PersistentVolumeClaims (PVCs) on different ONTAP clusters, so that your data is always protected and available. Here’s why you should be excited about these mirror relationships:

Disaster recovery. With SnapMirror. your data is replicated and ready to go in case of any disaster.
Seamless failover. Easily promote secondary volumes during unplanned failovers and perform smooth transitions during planned migrations.
Custom Resource Definition (CRD). Manage mirror relationships effortlessly with the Trident Mirror Relationship (TMR) CRD.

Prerequisites: Ready, set, go!

Before we get started, make sure that you have the following in place:

ONTAP clusters: Both source and destination clusters must have ONTAP SnapMirror asynchronous licenses enabled. Refer to SnapMirror licensing overview in ONTAP for more information. To use Trident SnapMirror Volume Replication with NVMe/TCP, the ONTAP version must be 9.15.1 or later.
Create a cron job on the destination cluster for an asynchronous replication schedule, Example command:
```
cron create -name five_minute -minute 0,5,10,15,20,25,30,35,40,45,50,55
```

Peering: ONTAP clusters are in cluster peering, and the storage virtual machines (SVMs) of the source and destination clusters are in vserver peering.
Trident. Trident version should be 25.06 or later.

Setting up SnapMirror volume replication for NVMe/TCP with a step-by-step example.

Create Trident back end for source cluster. Start by creating a Trident back end with the storage driver ontap-san. You can do this either by configuring the TridentBackendConfig (TBC) custom resource definition using the Kubernetes-native approach or by using a custom JSON file with tridentctl, a command-line utility for managing Trident. The configuration is similar to any other ontap-san NVMe back end, with the only changes being the username and password. You can either use a cluster management IP with administrator credentials or specify a storage virtual machine with its management IP and credentials. For more information, refer to ONTAP SAN driver details.
```
# Kubernetes secret required for creating Trident backend from TBC
[root@scs000646264 artifacts]# cat primary-secret.yaml
apiVersion: v1
kind: Secret
metadata:
name: primary-tbc-secret
type: Opaque
stringData:
username: <username>
password: <password>
 
[root@scs000646264 artifacts]# kubectl create -f primary-secret.yaml -n trident
secret/primary-tbc-secret created
```

Add the back end. When the back end is configured, you can add it to Trident by using either kubectl or tridentctl. These tools are a convenient way to add the newly configured back end to Trident and make it available for use.

# Kubernetes CR TridentBackendConfig (TBC)
[root@scs000646264 artifacts]# cat primary-tbc.yaml---
apiVersion: trident.netapp.io/v1
kind: TridentBackendConfig
metadata:
  name: primary-backend-tbc
spec:
  version: 1
  storageDriverName: ontap-san
  sanType: nvme
  managementLIF: 8.8.8.8
  svm: svm0
  credentials:
    name: primary-tbc-secret

[root@scs000646264 artifacts]# kubectl create -f primary-tbc.yaml -n trident
tridentbackendconfig.trident.netapp.io/primary-backend-tbc created

[root@scs000646264 artifacts]# kubectl get tbc -n trident
NAME                    BACKEND NAME            BACKEND UUID                           PHASE   STATUS
primary-backend-tbc     primary-backend-tbc     a9b1a3a7-66a8-4d3b-984a-b87d851387c7   Bound   Success

# Or, Trident backend json
[root@scs000646264 artifacts]# cat backend.json 
{
    "version": 1,
    "storageDriverName": "ontap-san",
    "managementLIF": "8.8.8.8",
    "backendName": "primary-backend"
    "svm": "svm0",
    "username": "<username>",
    "password": "<password>",
    "sanType": "nvme"
}

[root@scs000646264 artifacts]# tridentctl create b -f primary-backend.json -n trident
+--------------------+----------------+--------------------------------------+--------+------------+---------+
|        NAME        | STORAGE DRIVER |                 UUID                 | STATE  | USER-STATE | VOLUMES |
+--------------------+----------------+--------------------------------------+--------+------------+---------+
| primary-backend    | ontap-san      | 6458337e-a27e-4cde-8707-0f6218214356 | online | normal     |       0 |
+--------------------+----------------+--------------------------------------+--------+------------+---------+

Define a storage class. Create a storage class that corresponds to the type of storage driver you need. This step allows you to define the characteristics of the storage that you want to dynamically provision.

kind: StorageClass
metadata:
  name: primary-sc
provisioner: csi.trident.netapp.io
parameters:
  backendType: ontap-san
  storagePools: primary-backend-tbc:.*
allowVolumeExpansion: true

root@scs000646264 artifacts]# kubectl create -f primary-sc.yaml 
storageclass.storage.k8s.io/primary-sc created

[root@scs000646264 artifacts]# kubectl get sc
NAME           PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE   ALLOWVOLUMEEXPANSION   AGE
primary-sc     csi.trident.netapp.io   Delete          Immediate           true                   2s

Create a PVC. Define a PersistentVolumeClaim that specifies the amount of storage you need and references the appropriate storage class. This step ensures that your Kubernetes application has access to the required block storage.

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: primary-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Mi
  storageClassName: primary-sc

[root@scs000646264 artifacts]# kubectl create -f primary-pvc.yaml 
persistentvolumeclaim/primary-pvc created&#8203;

Confirm PVC binding. After the PVC is created, verify that it’s successfully bound to a persistent volume (PV). This step confirms that the block storage is ready for use by your applications.

[root@scs000646264 artifacts]# kubectl get pvc
NAME          STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   VOLUMEATTRIBUTESCLASS   AGE
primary-pvc   Bound    pvc-bd77f21b-4522-41e9-bfa1-fca7cf8af672   20Mi       RWO            primary-sc     <unset>                 4s
&#8203;

Use the PVC. You’re now ready to use the PVC in any pod of your choice. Mount the PVC in a pod to store data.
The following example simulates an application workload. This pod runs an Nginx container, writing timestamps to a file on the PVC every 20 seconds.

[root@scs000646264 artifacts]# cat pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: source-pod
spec:
  containers:
    - image: nginx:alpine
      name: nginx
      volumeMounts:
        - mountPath: /pv/pvc
          name: local-storage
      command: ["/bin/ash", "-c"]
      args:
        - |
          while true; do
            echo `date +%Y-%m-%d.%H:%M:%S` >> /pv/pvc/data.txt;
            fsync /pv/pvc;
            fsync /pv/pvc/data.txt;
            tail -n 1 /pv/pvc/data.txt;
            sleep 20;
          done
  nodeSelector:
    kubernetes.io/arch: amd64
    kubernetes.io/os: linux
  volumes:
    - name: local-storage
      persistentVolumeClaim:
        claimName: primary-pvc
[root@scs000646264 artifacts]# kubectl create -f pod.yaml
pod/source-pod created


[root@scs000646264 artifacts]# kubectl get po
NAME         READY   STATUS              RESTARTS   AGE
source-pod   1/1     Running             0          15s

[root@scs000646264 artifacts]# kubectl logs source-pod
2025-05-21.07:30:12
2025-05-21.07:30:32

Create source MirrorRelationship custom resource (CR) with local information (localPVCName).
Trident fetches the internal information for the volume and the volume’s current data protection (DP) state, then populates the status field of the MirrorRelationship.

kind: TridentMirrorRelationship
apiVersion: trident.netapp.io/v1
metadata:
name: source-tmr
spec:
state: promoted
volumeMappings:
- localPVCName: primary-pvc

[root@scs000646264 artifacts]# kubectl create -f source-tmr.yaml 
tridentmirrorrelationship.trident.netapp.io/source-tmr created

[root@scs000646264 artifacts]# kubectl get tmr
NAME         DESIRED STATE   LOCAL PVC     ACTUAL STATE   MESSAGE
source-tmr   promoted        primary-pvc   promoted      
&#8203;

Get the TridentMirrorRelationship CR to obtain the internal name and SVM of the PVC.

[root@scs000646264 artifacts]# kubectl get tmr source-tmr -o yaml
apiVersion: trident.netapp.io/v1
kind: TridentMirrorRelationship
metadata:
  creationTimestamp: "2025-05-21T07:26:15Z"
  finalizers:
  - trident.netapp.io
  generation: 2
  name: source-tmr
  namespace: default
  resourceVersion: "4573176"
  uid: 7d0cb8e2-434a-4c1b-b3a8-8d181f744f82
spec:
  replicationPolicy: ""
  replicationSchedule: ""
  state: promoted
  volumeMappings:
  - localPVCName: primary-pvc
    promotedSnapshotHandle: ""
    remoteVolumeHandle: ""
status:
  conditions:
  - lastTransitionTime: "2025-05-21T07:26:15Z"
    localPVCName: primary-pvc
    localVolumeHandle: svm0:trident_pvc_bd77f21b_4522_41e9_bfa1_fca7cf8af672
    message: ""
    observedGeneration: 2
    remoteVolumeHandle: ""
    replicationPolicy: ""
    replicationSchedule: ""
    state: promoted&#8203;

Perform the following steps for the destination cluster:
Create Trident back end with a replicationPolicy of MirrorAllSnapshots.

# Kubernetes secret required for creating Trident backend from TBC
[root@scs000646264 artifacts]# cat secondary-secret.yaml
apiVersion: v1
kind: Secret
metadata:
  name: secondary-tbc-secret
type: Opaque
stringData:
  username: <username>
  password: <password>


[root@scs000646264 artifacts]# kubectl create -f secondary-secret.yaml -n trident
secret/secondary-tbc-secret created


[root@scs000646264 artifacts]# cat secondary-tbc.yaml
apiVersion: trident.netapp.io/v1
kind: TridentBackendConfig
metadata:
  name: secondary-backend-tbc
spec:
  version: 1
  storageDriverName: ontap-san
  sanType: nvme
  managementLIF: 7.7.7.7
  svm: svm1
  replicationPolicy: MirrorAllSnapshots
  replicationSchedule: five_minute
  credentials:
    name: secondary-tbc-secre

[root@scs000646264 artifacts]# kubectl create -f secondary-tbc-tamu.yaml -n trident
tridentbackendconfig.trident.netapp.io/secondary-backend-tbc created

[root@scs000646264 artifacts]# kubectl get tbc -n trident
NAME                    BACKEND NAME            BACKEND UUID                           PHASE   STATUS
primary-backend-tbc     primary-backend-tbc     a9b1a3a7-66a8-4d3b-984a-b87d851387c7   Bound   Success
secondary-backend-tbc   secondary-backend-tbc   c4fbde1a-cf6c-4ee4-8474-488454c926d1   Bound   Success


# Or, Trident backend json
[root@scs000646264 artifacts]# cat backend.json 
{
    "version": 1,
    "storageDriverName": "ontap-san",
    "managementLIF": "7:7:7:7",
    "backendName": "secondary-backend"
    "svm": "svm0",
    "username": "<username>",
    "password": "<password>",
    "sanType": "nvme"
    "replicationPolicy": "MirrorAllSnapshots"
    "replicationSchedule": "five_minute"
}

[root@scs000646264 artifacts]# tridentctl create b -f primary-backend.json -n trident
+--------------------+----------------+--------------------------------------+--------+------------+---------+
|        NAME        | STORAGE DRIVER |                 UUID                 | STATE  | USER-STATE | VOLUMES |
+--------------------+----------------+--------------------------------------+--------+------------+---------+
| secondary-backend    | ontap-san    | 2345337e-e67e-4bdm-8707-1d5644326548 | online | normal     |       0 |
+--------------------+----------------+--------------------------------------+--------+------------+---------+

Create destination storage class.

[root@scs000646264 artifacts]# cat secondary_sc.yaml 
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: secondary-sc
provisioner: csi.trident.netapp.io
parameters:
  backendType: ontap-san
  storagePools: secondary-backend-tbc:.*
allowVolumeExpansion: true

[root@scs000646264 artifacts]# kubectl create -f secondary_sc.yaml 
storageclass.storage.k8s.io/secondary-sc created

[root@scs000646264 artifacts]# kubectl get sc
NAME           PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE   ALLOWVOLUMEEXPANSION   AGE
primary-sc     csi.trident.netapp.io   Delete          Immediate           true                  11s
secondary-sc   csi.trident.netapp.io   Delete          Immediate           true                   3s

Create destination PVC with previously created StorageClass to act as the secondary (SnapMirror destination).
Trident checks for the TridentMirrorRelationship CRD. If the relationship does not exist, Trident fails to create the volume and remains in pending state until the destination TMR is created.
If the relationship exists, Trident places the new FlexVol volume onto an SVM that is peered with the remote SVM defined in the MirrorRelationship.

[root@scs000646264 artifacts]# cat secondary-pvc.yaml
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  annotations:
    trident.netapp.io/mirrorRelationship: dest-tmr
  name: secondary-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Mi
  storageClassName: secondary-sc

[root@scs000646264 artifacts]# kubectl create -f secondary-pvc.yaml 
persistentvolumeclaim/secondary-pvc created

[root@scs000646264 artifacts]# kubectl get pvc 
NAME            STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   VOLUMEATTRIBUTESCLASS   AGE
primary-pvc     Bound     pvc-bd77f21b-4522-41e9-bfa1-fca7cf8af672   20Mi       RWO            primary-sc     <unset>                 43s
secondary-pvc   Pending                                                                        secondary-sc   <unset>                 4s

Create destination TMR CR.
Trident creates a SnapMirror relationship with the configured relationship policy name (or default for ONTAP) and initializes it. (Provide the value obtained in “Get the TridentMirrorRelationship CR to obtain the internal name and SVM of the PVC,” earlier in this document, as the remoteVolumeHandle in destination TMR CR.)

kind: TridentMirrorRelationship&rdquo;
apiVersion: trident.netapp.io/v1
metadata:
  name: dest-tmr
spec:
  state: established
  volumeMappings:
    - localPVCName: secondary-pvc
      remoteVolumeHandle: "svm0:trident_pvc_bd77f21b_4522_41e9_bfa1_fca7cf8af672"

[root@scs000646264 artifacts]# kubectl create -f dest-tmr.yaml 
tridentmirrorrelationship.trident.netapp.io/dest-tmr created 

[root@scs000646264 artifacts]# kubectl get tmr
NAME         DESIRED STATE   LOCAL PVC       ACTUAL STATE   MESSAGE
source-tmr   promoted        primary-pvc     promoted       
dest-tmr     established     secondary-pvc   established    
&#8203;

Verify the SnapMirror relationship and volume type (DP) on the destination cluster:

stiA300-2491746692774::> snapmirror show
                                                                       Progress
Source            Destination Mirror  Relationship   Total             Last
Path        Type  Path        State   Status         Progress  Healthy Updated
----------- ---- ------------ ------- -------------- --------- ------- --------
svm0:trident_pvc_bd77f21b_4522_41e9_bfa1_fca7cf8af672 
            XDP  svm1:trident_pvc_32d31b4d_ec91_41cd_a95e_9e74bd6b2d9b 
                              Snapmirrored 
                                      Idle           -         true    -



stiA300-2491746692774::> volume show -vserver svm1
Vserver   Volume       Aggregate    State      Type       Size  Available Used%
--------- ------------ ------------ ---------- ---- ---------- ---------- -----
svm1      svm0_root    stiA300_250_aggr1 
                                    online     RW          1GB    972.4MB    0%
svm1      trident_pvc_32d31b4d_ec91_41cd_a95e_9e74bd6b2d9b 
                       stiA300_249_aggr1 
                                    online     DP         22MB    20.42MB    7%
2 entries were displayed.
&#8203;

Create snapshot class

[root@scs000646264 artifacts]# cat snapshot-class.yaml
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: csi-snapclass
driver: csi.trident.netapp.io
deletionPolicy: Delete


[root@scs000646264 artifacts]# kubectl create -f snapshot-class.yaml
volumesnapshotclass.snapshot.storage.k8s.io/csi-snapclass created

[root@scs000646264 artifacts]#  kubectl get volumesnapshotclasses 
NAME            DRIVER                  DELETIONPOLICY   AGE
csi-snapclass   csi.trident.netapp.io   Delete           5s

Below is the output for the snapshot show command in the Destination cluster, Before any snapshot is created.

stiA300-2491746692774::> snapshot show
                                                                 ---Blocks---
Vserver  Volume   Snapshot                                  Size Total% Used%
-------- -------- ------------------------------------- -------- ------ -----
svm1     trident_pvc_32d31b4d_ec91_41cd_a95e_9e74bd6b2d9b
                  snapmirror.33ffbac2-300c-11f0-8dc5-00a098f48d3e_2155208310.2025-05-21_032847 
                                                           216KB     1%   40%
                  snapmirror.33ffbac2-300c-11f0-8dc5-00a098f48d3e_2155208310.2025-05-21_033000 
                                                           136KB     1%   29%
2 entries were displayed.
&#8203;

Create snapshot

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
name: "snap1"
spec:
volumeSnapshotClassName: csi-snapclass
source:
persistentVolumeClaimName: primary-pvc

root@scs000646264 artifacts]# kubectl create -f snapshot.yaml 
volumesnapshot.snapshot.storage.k8s.io/snap1 created

[root@scs000646264 artifacts]# kubectl get volumesnapshots
NAME    READYTOUSE   SOURCEPVC     SOURCESNAPSHOTCONTENT   RESTORESIZE   SNAPSHOTCLASS   SNAPSHOTCONTENT                                    CREATIONTIME   AGE
snap1   true         primary-pvc                           20Mi          csi-snapclass   snapcontent-7a3b0380-6d13-4cb9-88a3-df9528be73a9   5s             6s

Output of the snapshot show command in the destination cluster after the first Snapshot copy is taken:

stiA300-2491746692774::> snapshot show
                                                                 ---Blocks---
Vserver  Volume   Snapshot                                  Size Total% Used%
-------- -------- ------------------------------------- -------- ------ -----
svm1     trident_pvc_32d31b4d_ec91_41cd_a95e_9e74bd6b2d9b
                  snapmirror.33ffbac2-300c-11f0-8dc5-00a098f48d3e_2155208310.2025-05-21_033000 
                                                           216KB     1%   19%
                  snapshot-7a3b0380-6d13-4cb9-88a3-df9528be73a9 
                                                           268KB     1%   22%
                  snapmirror.33ffbac2-300c-11f0-8dc5-00a098f48d3e_2155208310.2025-05-21_033740 
                                                           180KB     1%   16%
3 entries were displayed.&#8203;

Working with more Snapshot copies:

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
name: "snap1-new"
spec:
volumeSnapshotClassName: csi-snapclass
source:
persistentVolumeClaimName: primary-pvc

root@scs000646264 artifacts]#  kubectl create -f snapshot-1.yaml 
volumesnapshot.snapshot.storage.k8s.io/snap1-new created

[root@scs000646264 artifacts]# kubectl get vs
NAME        READYTOUSE   SOURCEPVC     SOURCESNAPSHOTCONTENT   RESTORESIZE   SNAPSHOTCLASS   SNAPSHOTCONTENT                                    CREATIONTIME   AGE
snap1       true         primary-pvc                           20Mi          csi-snapclass   snapcontent-7a3b0380-6d13-4cb9-88a3-df9528be73a9   6m33s          6m34s
snap1-new   true         primary-pvc                           20Mi          csi-snapclass   snapcontent-56cf40dc-f968-4aeb-9ffd-ea1f7bcf0942   4s             5s

Snapshots transfer ensures the replication process.

stiA300-2491746692774::> snapshot show
                                                                 ---Blocks---
Vserver  Volume   Snapshot                                  Size Total% Used%
-------- -------- ------------------------------------- -------- ------ -----
svm1     trident_pvc_32d31b4d_ec91_41cd_a95e_9e74bd6b2d9b
                  snapshot-7a3b0380-6d13-4cb9-88a3-df9528be73a9 
                                                           268KB     1%   20%
                  snapmirror.33ffbac2-300c-11f0-8dc5-00a098f48d3e_2155208310.2025-05-21_033740 
                                                           276KB     1%   21%
                  snapshot-56cf40dc-f968-4aeb-9ffd-ea1f7bcf0942 
                                                           264KB     1%   20%
                  snapmirror.33ffbac2-300c-11f0-8dc5-00a098f48d3e_2155208310.2025-05-21_034000 
                                                           272KB     1%   21%
4 entries were displayed.
&#8203;

In Trident, when the state of the destination TMR is established, it indicates that the destination volume is a Data Protection (DP) volume. DP volumes are used for replication and backup, so that your data is protected and can be recovered in case of failure.
To verify that the destination volume is indeed a DP volume, you can use the volume show command:

stiA300-2491746692774::> volume show
Vserver   Volume       Aggregate    State      Type       Size  Available Used%
--------- ------------ ------------ ---------- ---- ---------- ---------- -----
stiA300-249 
          vol0         aggr0_stiA300_249 
                                    online     RW      348.6GB    291.9GB   11%
stiA300-250 
          vol0         aggr0_stiA300_250 
                                    online     RW      348.6GB    291.7GB   11%
svm1      svm0_root    stiA300_250_aggr1 
                                    online     RW          1GB    972.4MB    0%
svm1      trident_pvc_32d31b4d_ec91_41cd_a95e_9e74bd6b2d9b 
                       stiA300_249_aggr1 
                                    online     DP         22MB    19.93MB    9%
vs0       root_vs0     stiA300_249_aggr1 
                                    online     RW          1GB    972.1MB    0%
5 entries were displayed.

Volume replication states

The TMR CRD has the following states to manage the replication relationship:

Established. When the state of destination TMR is established, it indicates that the destination volume is a Data Protection (DP) volume. DP volumes are used for replication and backup, so that your data is protected and can be recovered in case of failure.
Promoted. When the TMR state is promoted, it indicates that the destination volume has been elevated to become the new source volume. This means that the destination volume is now writable and can serve I/O operations, effectively taking over the role of the original source volume.
Reestablished. The TMR state is reestablished after failover when the original source volume is ready to resume its role as the primary volume. This typically occurs in scenarios where the original issue that caused the failover has been resolved or maintenance has been completed, and you want to revert the roles of the source and destination volumes to their original configuration. When the TMR state is reestablished, it indicates that the replication relationship between the source and destination volumes has been restored to its original state.

Promote secondary PVC during an unplanned failover
Perform the following step on the secondary Kubernetes cluster:
Update the spec.state field of TridentMirrorRelationship to promoted.

kind: TridentMirrorRelationship
apiVersion: trident.netapp.io/v1
metadata:
  name: dest-tmr
spec:
  state: promoted
  volumeMappings:
    - localPVCName: secondary-pvc
      remoteVolumeHandle: "svm0:trident_pvc_bd77f21b_4522_41e9_bfa1_fca7cf8af672"
[root@scs000646264 artifacts]# kubectl apply -f dest-tmr.yaml 
tridentmirrorrelationship.trident.netapp.io/dest-tmr configured


[root@scs000646264 artifacts]# kubectl get tmr
NAME         DESIRED STATE   LOCAL PVC       ACTUAL STATE    MESSAGE
source-tmr   promoted        primary-pvc     promoted          
dest-tmr     promoted        secondary-pvc   promoted

Once the destination TMR is promoted, the destination volume becomes the RW volume with no mirror relationship currently in effect.

Check the volume state and snapmirror:

stiA300-2491746692774::> snapmirror show
This table is currently empty.
stiA300-2491746692774::> volume show
Vserver   Volume       Aggregate    State      Type       Size  Available Used%
--------- ------------ ------------ ---------- ---- ---------- ---------- -----
stiA300-249 
          vol0         aggr0_stiA300_249 
                                    online     RW      348.6GB    291.9GB   11%
stiA300-250 
          vol0         aggr0_stiA300_250 
                                    online     RW      348.6GB    291.7GB   11%
svm1      svm0_root    stiA300_250_aggr1 
                                    online     RW          1GB    972.4MB    0%
svm1      trident_pvc_32d31b4d_ec91_41cd_a95e_9e74bd6b2d9b 
                       stiA300_249_aggr1 
                                    online     RW         22MB    19.93MB    9%
vs0       root_vs0     stiA300_249_aggr1 
                                    online     RW          1GB    972.1MB    0%
5 entries were displayed.

When TMR is in promoted state, you can mount applications with the destination PVC.
Test the promoted PVC by mounting it in a pod:

apiVersion: v1
kind: Pod
metadata:
  name: test-pod
spec:
  containers:
    - name: test-container
      image: nginx:alpine
      imagePullPolicy: IfNotPresent
      volumeMounts:
        - mountPath: /mnt/test-path
          name: test-volume
          readOnly: false
  restartPolicy: Never
  volumes:
    - name: test-volume
      persistentVolumeClaim:
        claimName: secondary-pvc
        readOnly: false

[root@scs000646264 artifacts]# kubectl create -f test-pod.yaml 

[root@scs000646264 artifacts]# kubectl get po 
NAME         READY   STATUS              RESTARTS   AGE
source-pod   1/1     Running             0          12m
test-pod     1/1     Running             0          8s

Restore a mirror relationship after a failover
The TMR state is reestablished after a failover or planned switchover operation when the original source volume is ready to resume its role as the primary volume.

kind: TridentMirrorRelationship
apiVersion: trident.netapp.io/v1
metadata:
  name: dest-tmr
spec:
  state: reestablished
  volumeMappings:
    - localPVCName: secondary-pvc
      remoteVolumeHandle: "svm0:trident_pvc_bd77f21b_4522_41e9_bfa1_fca7cf8af672"

[root@scs000646264 artifacts]# kubectl apply -f dest-tmr.yaml 
tridentmirrorrelationship.trident.netapp.io/dest-tmr configured

snapmirror show output:

stiA300-2491746692774::> snapmirror show
                                                                       Progress
Source            Destination Mirror  Relationship   Total             Last
Path        Type  Path        State   Status         Progress  Healthy Updated
----------- ---- ------------ ------- -------------- --------- ------- --------
svm0:trident_pvc_bd77f21b_4522_41e9_bfa1_fca7cf8af672 
            XDP  svm1:trident_pvc_32d31b4d_ec91_41cd_a95e_9e74bd6b2d9b 
                              Snapmirrored 
                                      Idle           -         true    -

Conclusion: Your data, unstoppable!

With NetApp Trident and SnapMirror, you’ve built a robust disaster recovery pipeline for your Kubernetes applications. Every file—secrets, back ends, storage classes, PVCs, TMRs, Snapshot copies, and pods—plays a critical role in making sure that your data is replicated, protected, and ready for any scenario. Follow the steps in this guide and your clusters will be prepared to handle disasters with confidence.

Additionally, check out Trident protect, which helps you to manage SnapMirror and fail over the data, and also to manage the complete application. For more detailed information on using SnapMirror replication with Trident protect, check out the NetApp Trident protect documentation.

Want to dive deeper? Check out the NetApp Trident documentation for more insights. Happy replicating!

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