We are replacing our FAS6210's with FAS8020's. Due to the limited number of PCI expansion slots we will be using a Flash Pool with 200 GB SSD's. Will 4 x 200 GB SSD's roughly replace the I/O performance of 512 GB of PAM/Flash Cache? This is for a single aggregate of 60 SATA drives.
Without getting too deep in the weeds the performance of caching with Flash Cache over Flash Pools is very similar. However you get some additional benefits w/ FlashPool as it's persistent and does not require the flash to rewarm upon system failover. You also get the benefits of random overwrite caching (this is something we don't do with FlashCache). If the system will be running clustered Data ONTAP you will also get some additional benefits if your deploying the Flash Pool with version 8.3 of ONTAP. I can't mention those here but if you contact your local team they can get you in contact with an NDA presenter to share those benefits with you.
To cache the same amount of data as a 512GB Flash Cache card can hold, you will need four 200GB SSDs for data plus one parity drive and one hot spare.
In the industry, SSD and HDD capacities are stated in decimal (base10) values; the 512GB Flash Cache card capacity is a binary (base2) value, which is 7% larger. In addition, cache metadata for Flash Pool is stored on the SSDs whereas Flash Cache metadata is kept in controller main memory.