OK, I see what you are saying.
If you lose A or B, you are still in the realms of having to re-baseline Ca or Cb becasue losing A or B means losing the base snapshot in the source, however where you gain in this model is that Ca and Cb will benefit from aggregate deduplication so there is no negative impact on capacity.
Let's say for example I lose A and have to re-baseline to Ca, I was under the impression that I also lose the snapshots that I want retained at Ca to support the SLA for snapshot retention.
wrote: if A going down for a week - the base snapshot used to Ca is kept.
Is that really the case if you SM-S (re)sync B to A?