Sorry but my reply is correct even though it may not completely address that two year old question. Because of hardware (and firmware) differences one cannot upgrade OR downgrade to or from the v2.x firmware on a single bay My Cloud unit that does not support it. So one cannot take a first gen v3.x/v4.x firmware single bay My Cloud and put v2.x firmware on it. Nor can one take a second gen v2.x single bay My Cloud and put the first generation v3.x or v4.x firmware on it.
The only downgrade/upgrade one can do is with the first gen single bay My Cloud, and one can only go from v3.x to v4.x or from v4.x to v3.x. The main problem with the first gen My Cloud is due to WD (for some reason) using 64-bit page size early on with the v4.x firmware. The v3.x and v2.x firmware apparently do not use that page size. Furthermore it the hardware differences between the second gen My Cloud units and the first gen My Cloud units that also prevents (at present) attempting to use v2.x on the first gen single bay My Cloud.
Second gen single bay users can with some work enable the “apps” to certain third party apps found in the multi bay My Cloud units to run on the second gen My Cloud. For we first gen users we have the option to replace the OS entirely or use various unofficial mods to enable certain additional features.
Thanks to some ridiculous decision by someone at WD they used an earlier firmware number for the NEWER second generation single bay My Cloud units. This has often caused confusion where users think their newer second gen v2.x firmware is out of date or older than the older less capable/less featured v3.x/v4.x firmware.
