Would running two CP command to copy 2 different set of files to two different targets suffice as a basic two thread test?
So long as you generate disk access through a file system and not hdparm.
Is there a way to monitor actual disk transfers from command line without having to do manual timing?
Like I said: iostat
iostat -m 1 iostat -x 1 iostat -d 1 iostat -xm 1
Choose whatever information/data you fancy.
In fact, let me just post some iostat output to settle this once and for all. I shall risk the annoyance of all by attaching the output of a 'iostat -m sda sdb md1 1' command.
This was generated by a single Linux client connected via cifs do a cp -r off the cifs remote share to local disk. The output was generated on the remote share box.
From the output, I guess one loses grounds for claiming that md raid1 only reads off one disk even if there are periods of time when it really does only read off one disk.