Add RetentionPolicy supporting limitation in documents.

Signed-off-by: Xun Jiang <[email protected]>

site/content/docs/main/backup-reference.md

@@ -63,6 +63,8 @@ This command will immediately trigger a new backup based on your template for `e
 
 
 ### Limitation
+
+#### Backup's OwnerReference with Schedule
 Backups created from schedule can have owner reference to the schedule. This can be achieved by command:
 
 ```
@@ -74,7 +76,16 @@ Please do notice there is also side effect that may not be expected. Because sch
 
 If there is possibility the schedule will be disable to not create backup anymore, and the created backups are still useful. Please do not enable this option. For detail, please reference to [Backups created by a schedule with useOwnerReferenceInBackup set do not get synced properly](https://github.com/vmware-tanzu/velero/issues/4093).
 
+#### Cannot support backup data immutability
+From Velero's release-1.11 branch, Velero cannot support backup data immutability in Object Storage. Because Velero introduced a `Finalizing` state, Velero will first enter `Finalizing` phase after backup completion, and then the Finalizing controller will check whether there is any async operation in progress. If there is, then Velero will wait for all async operations complete, then turn backup into `Complete` phase. If there is not, then Velero will turn into `Complete` directly.
+
+By current design, whether there is async operation included or not, Velero's metadata in the OSS needs to change after it's created.
 
+The following is the cloud providers' documents:
+* [AWS S3 Using S3 Object Lock](https://docs.aws.amazon.com/AmazonS3/latest/userguide/object-lock.html)
+* [Azure Storage Blob Containers - Lock Immutability Policy](https://learn.microsoft.com/en-us/rest/api/storagerp/blob-containers/lock-immutability-policy?tabs=HTTP)
+* [GCP cloud storage Retention policies and retention policy locks](https://cloud.google.com/storage/docs/bucket-lock)
+
 ## Kubernetes API Pagination
 
 By default, Velero will paginate the LIST API call for each resource type in the Kubernetes API when collecting items into a backup. The `--client-page-size` flag for the Velero server configures the size of each page.

site/content/docs/v1.11/backup-reference.md

@@ -63,6 +63,7 @@ This command will immediately trigger a new backup based on your template for `e
 
 
 ### Limitation
+#### Backup's OwnerReference with Schedule
 Backups created from schedule can have owner reference to the schedule. This can be achieved by command:
 
 ```
@@ -74,6 +75,15 @@ Please do notice there is also side effect that may not be expected. Because sch
 
 If there is possibility the schedule will be disable to not create backup anymore, and the created backups are still useful. Please do not enable this option. For detail, please reference to [Backups created by a schedule with useOwnerReferenceInBackup set do not get synced properly](https://github.com/vmware-tanzu/velero/issues/4093).
 
+#### Cannot support backup data immutability
+From Velero's release-1.11 branch, Velero cannot support backup data immutability in Object Storage. Because Velero introduced a `Finalizing` state, Velero will first enter `Finalizing` phase after backup completion, and then the Finalizing controller will check whether there is any async operation in progress. If there is, then Velero will wait for all async operations complete, then turn backup into `Complete` phase. If there is not, then Velero will turn into `Complete` directly. 
+
+By current design, whether there is async operation included or not, Velero's metadata in the OSS needs to change after it's created.
+
+The following is the cloud providers' documents:
+* [AWS S3 Using S3 Object Lock](https://docs.aws.amazon.com/AmazonS3/latest/userguide/object-lock.html)
+* [Azure Storage Blob Containers - Lock Immutability Policy](https://learn.microsoft.com/en-us/rest/api/storagerp/blob-containers/lock-immutability-policy?tabs=HTTP)
+* [GCP cloud storage Retention policies and retention policy locks](https://cloud.google.com/storage/docs/bucket-lock)
 
 ## Kubernetes API Pagination