Small as in form factor -- The NetApp EF550 is only 2RU in size and can house up to 24 SSDs.
Small as in smallest configuration of usable flash -- An All Flash FAS (AFF) would need to have a minimum of 6 disks for cDOT root aggregates (3x per node) and then enough SSD's to accomodate the necessary usable capacity configure with RAID-DP.
An EF550 can leverage multiple raid types and you can customize the number of SSD's you order in the configuration. In FAS configs you typically are ordering disks in sets of 12 or 24 to create sets of equal raid groups.
Hope this helps -- let me know if I can provide more information.
Jodey's response assumed you were asking about all-flash arrays.
The smallest SSD available for use in FAS systems - as either cache for Flash Pool aggregates or for all-SSD aggregates - is 200GB. Modular FAS systems (e.g. FAS8000s) can also be configured with PCIe-based Flash Cache cards in the controller to provide hybrid flash-HDD storage; the smallest Flash Cache card is 512GB.