Technical Report TR-3326 for Snapmirror gives the Best Practice advice for minimum 512MB NVRAM size when using Snapmirror sync/async
SnapMirror Sync and SnapMirror Semi-Sync are supported on any FAS or V-Series platform. However, low-NVRAM platforms such as those having 256MB or less NVRAM per controller are not recommended. Recommended platforms are those having 512MB or more NVRAM per controller.
A FAS2040 system has 512MB NVMEM which seems to be fine if the system is driven as a Standalone system.
What about a FAS2040 Cluster system. Here we end up having only 256MB NVMEM usable.
I would expect in this case we miss the Best Practice recommendation an it would'nt be a good idea to run such an environment.