Compellent Sizing

Hi

Apologies if this is an obvious question, but we are struggling to get an answer from Dell on this.

We are coming from EQL's where we were told to leave 5-10% free space for normal SAN operation, is this is the same on the SC2020 range? As I understand it snapshots every day to then work out its RAID striping/what data should be on 10 or 5. 

Our change rate is around 4TB/day, so would this mean we need at least 4TB free at all times to allow this to work?

Ta