With copy mode enabled, each restore point which gets created on performance tier will also be offloaded directly to the capacity tier. After 365 days, they will be removed from the performance tier.
This configuration doesn’t work for your goal. You can‘t keep 12 monthlies only on the performance tier, if you have enabled copy policy. They will instantly be copied to the capacity tier after their creation.
Do you have configured weekly fullbackup or just monthly ones? Without regular weekly fulls, you won‘t have just 7-14 daily backups, you will have 30-60 daily backups on both tiers. That‘s because your backup chains will have a size of one full and 29-30 incremental backups.
My recommendation, use copy mode and set the move mode to 7-14 days. If you use AWS or Azure, you can also offload the yearly backups to archive object storage to save money.
will the GFS monthly backup file size equal to full backup size, or only the first monthly full is full size, remaining 11 is like incremental file size? Same go to the GFS yearly backup file size over 10 years.
Object storage behaves like a forever forward incremental chain. Meaning the first offload will be a full offload. After that, only new unique blocks will be offloaded. This is also valid for synthetic/active backups and for gfs restore points. You won‘t see 22 times the size of a fullbackup in the capacity tier.
Thanks
Fabian