Merge pull request #10430 from Lyndon-Li/enhance-doc-for-backup-deletion

Enhance the doc for backup deletion

changelogs/unreleased/10430-Lyndon-Li

@@ -0,0 +1 @@
+Enhance the doc for backup deletion

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

@@ -161,7 +161,12 @@ Pagination can be entirely disabled by setting `--client-page-size` to `0`. This
 
 ## Deleting Backups
 
-Use the following commands to delete Velero backups and data:
+Use the following commands to delete Velero backups:  
+`velero backup delete <backupName>`: successful run of this command will:
+- Immediately delete the resource backup data from the backup storage
+- Immediately delete the volume snapshots associates to the backup if any (e.g., volumes are backed up with CSI snapshot backup or native snapshot method)
+- Trigger the deletion of volume backup data if any data is persisted to the backup repository (e.g., volumes are backed up with CSI snapshot data movement or fs-backup method). You will not see the backup storage space is released immediately, the backup repository maintenance jobs will GC the data and finally release the storage space
 
-* `kubectl delete backup <backupName> -n <veleroNamespace>` will delete the backup custom resource only and will not delete any associated data from object/block storage
-* `velero backup delete <backupName>` will delete the backup resource including all data in object/block storage
+Velero backup deletion needs extra spaces in the backup storage, so make sure the backup storage is not full during the backup deletion, otherwise, the backup deletion or the following backup repository maintenance jobs may fail.  
+
+`kubectl delete backup <backupName> -n <veleroNamespace>`: this command will delete the backup custom resource only and will not delete any associated data from the backup storage. So it is used for limited purposes only, e.g., all the backup data has been deleted in the backup storage, you just need to clear the orphaned CRs in the cluster.