You have a few options. One is to clone the old drive to the new drive then using Linux, expand the one EXT4 formatted partition on the new drive to cover the unused capacity on the new drive.
Or do what many have done and use Fox_EXE’s directions. Note one has to ensure they have a first gen (P/N number on the bottom of the single bay My Cloud enclosure ends with “P/N: WDBCTLxxxxxxx- 00”.
Use Linux or a Linux Boot Disk/Boot Flash Drive if possible. Do not change the values for the partition sizes when doing the mkpart section. After unbrick one usually gets a red LED upon first boot. Typically the My Cloud Dashboard will be accessable where one goes to the Settings > Utilities > System Factory Restore > System Only restore.
@Fox_exe Sorry for necroposting, but I need your help.
I also did a rebuild on the my cloud gen1 and updated with a bigger HDD. I also managed to install successfully clean debian and other packages that i need for the Jessie distro. It appears, that I one of the devices that suffers for not being able to negotiate a gigabit connection (at all). All attempts with ethtool (c2000-geth nic driver actually does not support half of what ethtool can do) leaded to mostly being able to have fast ethernet. I tried with 3 gigabit routers, 3 gigabit switches and different cables cat5a&6. So I decided to actually use a gigabit usb adapter (debian has the usbnet lib). Like for most gigabit adapters (ASIX chipset), the drivers need to be compiled. This is where i hung as the clean debian distro from your website is missing the linux headers for 3.2.68 - which are referenced in the Makefile of the usb driver. I tried to build the kernel (from wd) myself on a desktop machine with crosstools and failed miserably. Is there a possibility for you to also upload the headers? On your clean debian distro they are linking somewhere to /root - but that was probably from your desktop when you compiled. Or help me compile the driver? Ethernet to USB Adapter, USB 3.0 to RJ45 Gigabit Adapter – UGREEN - scroll down to the download section - [Driver_AX88179].
@Fox_exe Thanks for replying. I tried to compile your linked kernel 3.2.68 and build config, and also tried to follow your guide from here but with no success.
Which cross compile tool did you use? I generated one from here. Basically I only need the compiled linux headers.
Use WD compiler (From firmware sources).
Or install debian Jessie (Need old compiler for compile old kernel)
Also its possible to build kernel on device itself (“Native” build without cross-compilation)