Hi,
We haven't implemented Cloud Tiering yet but I was compelled to read about 'fabric-pool/storage-grid' after going through your email and this is what I observed.
In the fabric-pool documentation, it clearly states that - "Moving blocks back to the performance tier is not allowed."
FabricPool Documentation clearly states : "Changing the tiering policy from auto to snapshot-only or none does not cause active file system blocks that are already moved to the cloud tier to be moved back to the performance tier." In other words, once moved you cannot moved it back via 'changing policy'.
As I read, the only way to bring back (Inactive/cold Data-blocks) is either 'reads' or 'vol-move': As long as cloud-tier exists, "Volume reads" are needed for the data to be moved back to the performance tier. Which as I understand, unless the already moved blocks in the 'Cloud-Tier' are "read again", they will not come back to Performance tier. Interestingly, b'cos we are dealing at 'blocks-level' and not file-system level, we cannot decipher which folder/files are pointed to which blocks and therefore you have no control over which directory/file to "read-simulate" in order to bring those blocks back.
Another method is 'volume-move' (which I believe you have resorted to), Page:16 (Please read/something to watch out for) on this tr-4598 covers good info around 'volume-move' destination tier based on given 'tiering policy'.
Above information is based on the following documents:
https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-psmg%2FGUID-149A3242-B120-49CB-B712-BDDED53ED25D.html
https://www.netapp.com/us/media/tr-4598.pdf
https://whyistheinternetbroken.wordpress.com/tag/fabricpool/
Thanks!