Amazon S3 推出了新的 Storage Class，後面直接用演算法分析 access pattern (所以要跑一陣子才會生效)，然後決定要放到 Standard 或是 Standard IA 裡：「Announcing S3 Intelligent-Tiering — a New Amazon S3 Storage Class」。
混了 Standard 與 Standard IA：
S3 Intelligent-Tiering stores objects in two access tiers: one tier that is optimized for frequent access and another lower-cost tier that is optimized for infrequent access.
然後連續 30 天沒有被存取的就會被丟到 Standard IA，如果有被存取的話就會被搬回來，而搬移的部份不用收費：
For a small monthly monitoring and automation fee per object, S3 Intelligent-Tiering monitors access patterns and moves objects that have not been accessed for 30 consecutive days to the infrequent access tier. There are no retrieval fees in S3 Intelligent-Tiering. If an object in the infrequent access tier is accessed later, it is automatically moved back to the frequent access tier. No additional tiering fees apply when objects are moved between access tiers within the S3 Intelligent-Tiering storage class.
從費用上可以看到演算法本身是有費用的，換算一下 1M objects 是 USD$2.5/month，好像還可以...
Monitoring and Automation, All storage / Month $0.0025 per 1,000 objects
不過有蠻多要注意的 pattern。像是這邊有提到 128KB 以下的檔案不會搬到 IA 上，但不知道算不算 Monitoring 的費用？
S3 Intelligent-Tiering has a minimum eligible object size of 128KB for auto-tiering. Smaller objects may be stored but will always be charged at the Frequent Access tier rates.
另外這邊講 S3 Intelligent-Tiering 的三十天也不知道是不是 Standard + Standard IA，或是分開算：
S3 Intelligent-Tiering, S3 Standard-IA, and S3 One Zone-IA storage are charged for a minimum storage duration of 30 days.
可以先觀望一下...