Vectored insert does not support inserting into a capped collection, so if you do more than a light load of inserts into a capped collection, secondaries will flood their logs with:

2016-02-08T17:00:21.539-0500 E REPL     [repl writer worker 13] Error applying inserts in bulk  :: caused by :: 151 Can't batch inserts into indexed capped collections trying first insert as a lone insert

This also severely impacts performance since every batch insert throws and catches an exception.

We should avoid trying to do vector inserts on capped collections. We can use the CachingCappedChecker for this, or some other clever technique.