Hi,
On a very high-level:
- 7-Mode - either single controller, or two controllers clustered for HA; think of it as "traditional" ONTAP with all bells & whistles (dedupe, compression, cloning, etc.
- Cluster-Mode - either single controller *pair*, or multiple pairs connected (clustered) via back-end 10GbE network; it originates from ONTAP GX & basically the key thing is, you can have a single storage system with more than two controllers; there are some features specific for C-Mode (single namespace, Infinite Volumes, etc.), but some other features are still missed comparing to 7-Mode (e.g. SnapVault)
Regards,
Radek