This policy is used on the storage account that contains the backup copies of the Data Lake. This will apply retention of 60 days to the weekly backups, and retention of 30 days to the daily (incremental) backups.

backup_sta_lifecycle_policy_rules.json

{
  "rules": [
    {
      "enabled": true,
      "name": "weeklybackupsrule",
      "type": "Lifecycle",
      "definition": {
        "actions": {
          "baseBlob": {
            "delete": {
              "daysAfterModificationGreaterThan": 60
            }
          }
        },
        "filters": {
          "blobTypes": [
            "blockBlob"
          ],
          "prefixMatch": [
            "weekly"
          ]
        }
      }
    },
    {
      "enabled": true,
      "name": "dailybackupsrule",
      "type": "Lifecycle",
      "definition": {
        "actions": {
          "baseBlob": {
            "delete": {
              "daysAfterModificationGreaterThan": 30
            }
          }
        },
        "filters": {
          "blobTypes": [
            "blockBlob"
          ],
          "prefixMatch": [
            "daily"
          ]
        }
      }
    }
  ]
}