Hi all.
My 2TB My Book just got filled up and I’m willing to replace it with a bigger 4 TB disc.
Is it as simple as replacing the HDD inside the case or does it need any special procedure?
Thanks in advance 
If the drive is single bay then replacing the drive will lead to void the warranty of the drive because single bay drives are not user serviceable. Apart from that you if the drive is dual bay then you can change the drive directly as mention in the given article.
Hi and thanks for the reply!
I’m well passed the warranty time, so voiding the warranty is not something that worries me, but I wasn’t sure whether the system relies on a special formatting, or the disk might contain a software that makes the system work at all.
There are not WD official services close enough to send it to a proper service to get it done (it’s cheaper at this point buying a new one than paying for post & service), especially given the drive works flawlessly… just I got short on space… only 2GB free out of 2 TB 
