384GB or 768GB, have to check if we're using RDIMM or LRDIMM actually...To answer this post: https://forums.freenas.org/index.php?threads/what-are-your-arc-statistics.28122/page-9#post-330834 from @redbull666
Yes, the fact you only have
64 GB(wait: you said 64 GB but the stats show 32 GB, there's a problem somewhere...) of RAM for a 400 TB pool (that's a big pool BTW... :)) and your stats aren't exactly the best in the world tell me you definitely have some margin for improvement ;)
Are you maxed out on the RAM on this server?
The 32GB was ARC budgetted at that time, have actually increased that to 48GB recently. Considering the machine is doing more than managing the ZFS storage.