The command line noIndexBuildRetry flag will be removed in v4.2. Index builds cannot be arbitrarily aborted on a single replica set member with two-phase index builds in-progress. In v4.2 users will instead be able to abort in-progress index builds via killOp or dropIndexes against the primary. Slow startup due to waiting for index builds to finish will also no longer be of concern in v4.2 because startup will restart the index builds on separate threads and continue without waiting for them to finish (SERVER-37966).

Standalone mode nodes will neither recover nor discard any in-progress index builds if the node was previously a replica set member. The in-progress index builds will be ignored until the node is re-introduced to its replica set (SERVER-37637). In v4.0, standalone nodes always discarded all in-progress index builds, and an always standalone node restarted as standalone will continue to discard in-progress in v4.2. The noIndexBuildRetry flag therefore never had a use with standalone nodes in v4.0, and we do not want it to affect cross-replica set index builds present on standalones.