SSD Cache vs. Auto Tiering
The SSD cache and auto tiering solutions can work together and compliment each other. A key difference between tiering and cache is that tiering moves data to SSD instead of simply caching it. Tiering can also move data both from slower storage to faster storage and vice versa. However, SSD cache is essentially a one-way transaction. The important difference between moves and copies is that a cache does not need to have the redundancy that tiering does.
Total storage capacity in auto tiering is a sum of all individual tier capacities whereas in cache, the cache capacity does not add to the overall slower storage capacity. This is one of the key differences. In addition, SSD cache affects more rapidly than auto tiering because auto tiering will take effect after data relocation. So SSD cache warm-up timeframe is usually minutes/hours whereas tiering warm-up is usually days.
SSD cache is used for highly frequent data access environments and is effective short term, such as virtualization or video editing applications. However, auto tiering is used for predictable I/O workloads and is effective in long term. It's suitable for web, file, or email server applications.
||HDD + SSD
|When SSD is Damaged
||Pool Works Fine
||Effective in Short Term
||Effective in Long Term