Mongod Start-up time several parameter description

1.--storageengine
Starting from 3.0, a new storage engine WT was added. The old version of the storage engine is called MMAPV1

2.--oplogsize
Oplog is the primary component of replication and is located in the local database. When initializing the replica set, the disk space for the Oplog is pre-allocated, which defaults to 5% of the disk space.
The size of the oplog is important, and when the size is exceeded, the old document is emptied out. If it is too small, it can result in oplog data being discarded before replication is complete. Too much assembly results in wasted disk space and longer initialization time.
For the development environment, you can set a smaller point.

3.--shardsvr
Indicates that the server is started with Shard server.

4.--configsvr
To configure server startup.

5.--smallfiles
Primarily for development environments
By default, MongoDB will pre-create a 64m database file up to 2GB.
Using the "--smallfiles" parameter will only pre-allocate 16m of database files, the maximum file size can reach 512MB.
This parameter is not recommended for production environments

Mongod Start-up time several parameter description