Misc Performance Questions

[AJ]

Is there a performance hit when dropping a CF?  What if it contains .5 
TB of data?  If not, is there a quick and painless way to drop a large 
amount of data w/minimal perf hit?

Is there a performance hit running multiple keyspaces on a cluster 
versus only one keyspace given a constant total data size?  Is there 
some quantity limit?

Using a Random Partitioner, but with a RF = 1, will the rows still be 
spread-out evenly on the cluster or will there be an affinity to a 
single node (like the one receiving the data from the client)?

I see a lot of mention of using RAID-0, but not RAID-5/6.  Why?  Even 
though Cass can tolerate a down node due to data loss, it would still be 
more efficient to just rebuild a bad hdd live, right?

Maybe perf related:  Will there be a problem having multiple keyspaces 
on a cluster all with different replication factors, from 1-3?

Thanks!