I am trying to manually set usePowerOf2Sizes a new mongodb feature

The MongoDB doc's said the flag should be set with:

db.runCommand(

{collMod: "collection-name", usePowerOf2Sizes : true }

)

So in rails console after getting a Mongoid session, I ran the command below, where note_books is my collection name.

session.command(collMod: "note_books", userPowerOf2Sizes: true)

The command above throws the error

MOPED: 54.205.251.202:10056 COMMAND database=appt command={:collMod=>"note_books", :userPowerOf2Sizes=>true} runtime: 117.0294ms
Moped::Errors::OperationFailure: The operation: #<Moped::Protocol::Command
@length=87
@request_id=5
@response_to=0
@op_code=2004
@flags=[]
@full_collection_name="appt.$cmd"
@skip=0
@limit=-1
@selector={:collMod=>"note_books", :userPowerOf2Sizes=>true}
@fields=nil>
failed with error "unknown option to collMod: userPowerOf2Sizes"

If I change the command to use collmod instead of collMod

session.command(collmod: "note_books", userPowerOf2Sizes: true)

The error becomes failed with error "no such cmd: collmod"