Very few if any if your talking Cassandra (I would never store time series in redis), I worked developing TSD and are active in the space, most companies goes with Cassandra these days and builds computational frameworks upon that.
If you are at the scale you can't dump it on just 1-2 nodes and call it a day [which is when you are start looking at Cassandra or a dedicated TSD] ...you really need 3 DC availability usually and Redis simply cannot do that in any reasonable way.