let getBytesData x = 
    let len = reader.GetBytes(1, int64 0, null, 0, 0);
    // Create a buffer to hold the bytes, and then
    // read the bytes from the DataTableReader.
    let buffer : byte array = [||]
    reader.GetBytes(1, int64 0, buffer, 0, int32 len) |> ignore
    buffer

let retVal = List [ while reader.Read() do yield (reader.GetString(0), getBytesData reader, reader.GetDateTime(2)) ]

I have above code to read bytes[] from datareader.

getBytesData function takes reader and returns bytes[] from reader.

everything works fine but it getBytesData function is working very non-functional way.

Is there any way i can optimize in F#?

Sorry for kind of question, but i have started a new project on F# to squeeze all juice out of it, so trying to get each line most optimal way