Just one SSD for write-back cache, or when Tiering in Storage SPaces
It is painful that you can use SSD write-back cache just when Tiering is used. And when Tiering is used, same column size needs to be used for SSDs and HDDs, then its kinda expensive.
Matt Garson [MSFT] commented
A clarification - in R2, you can configure a write-back cache without configuring a tier. However, for best performance, we recommend using both the write-back cache and tiering.
We are aware of the challenges caused by the column count requirements in R2 and are investigating improvements in this area.