Question about delete column family.

i have 3 column families

cf.a - 1tb size
cf.b - 1tb size
cf.c - 1tb size

deletion is not immediate right? need to issue .Flush() command for it to be compacted correct?
if i delete cf.a, will read and write be affected with b and c? cf.a wont be used during the "Flush" / compaction process but will this affect b and c performance etc?
i was wondering if it's better to create column families and delete the cf or create 3 databases instead and delete 1 of the database (whichever is better)