The SmartTier enforcement operation ignores moving the shared extents. For example, consider a file A that contains some shared and private extents that belong to device 1. If the user sets a policy that states that all the extents of the file A must be allocated to device 2, the SmartTier enforcement operation moves all the non-shared extents from device 1 to device 2. However, the SmartTier enforcement operation ignores moving the shared extents. As a result, the file A still contains shared extents that belong to device 1. This occurs even after the successful execution of the SmartTier enforcement operation.
On the other hand, any subsequent new allocation on behalf of the file A adheres to the preset SmartTier policy. Since the copy-on-write or unshare operation requires a new allocation, the SmartTier enforcement operation complies with the preset policy. If a write operation on the file A writes to shared extents, new allocations as part of copy-on-write operation is done from device 2. This behaviour adheres to the preset SmartTier policy.