Hi,
Yesterday the harddisk of my Tyros4 crashed after a short period of making weird noise.
It's in the (3 year) warranty but I decided to put an SSD in.
Installation went perfect and took only a couple of minutes.
Since Yamaha choose the USB interface the type/brand of the drive is not critical.
For those who are interested I wrote a short guide "how to replace a Tyros4 drive"
It should be available at
https://www.yousendit.com/download/T2dlL0dKMHdveE04RmNUQw
Still I think it's a shame Yamaha did not use the SATA interface to get connected to the MB, but put an USB wire in between.