First of all, say hello as I did not find any thread for introducing myself. Second, sorry for my english skills as they are not very accurate, I'll try to do my best.
So, this is the workaround. I received a WD MyBook Live as christmas gift (1Tb), and first think that came to my mind has been to use it as Media Streamer server for all the devices in the house. But 1Tb HD is oversized for my requirements, and I decided to replace it by a Seagate 250Gb one (enough capacity for me, and I can reuse the 1Tb HD for other purposes).
I started reading this forum and all the things I've seen were related to unbrick, manually repartition the HD and so on, but I felt this was not my case. So, I started with another approach, and when I finished I realized that I did 90% of the things pointed by another guides but using only windows 7, so I'll share my experience here for the people that is not comfortable with Linux.
The reason I used Windows has been due to my inexperience with Linux and the problems generated by the last partition (dataVolume, partition 4). It was oversized (945Gb on a 250Gb disk) and the problems caused by part and fdisk commands, as they don't let me do anything. A Linux user can surely deal with this problem and suggest a solution, but this was not my case.
Sorry, no links as I cannot post them, but quick google search will bring you the programs. Replace " - " with "/" and you will go straight.
This method can be used for single HD units replacing the sector offset by the correct one, no matter the model of the unit. Don't really know if it can be used for mirrored models, but is theoretically possible if both destination disks are identical, simply repeat the procedure twice, one for each disk.
First of all, we need a working "source" HD (the one that comes with the unit), and it has to be configured at least one time. Don't know if this guide will work with an "out of the box" unit, without configuring it first. Probably yes.
1.- We have to dismount it from case and connect it to a USB adapter, free SATA port or anything else on W7 machine. Same for destination disk.
2.- Download "hddguru.com - software - HDD-Raw-Copy-Tool" - HDD Raw Copy Tool, this is an equivalent for linux DD but it clones the entire HD. It is not possible to define a range, but this is not a problem.
3.- Execute the program (as administrator, otherwise it won't show all devices) and select source HD (1Tb) and destination HD (250Gb in my case). Then start copy.
4.- Stop the copy at 12.000.000 sectors.
5.- Download "partitionwizard.com - free-partition-manager.html" - MiniTool Partition Manager, install and execute it. (Sorry, no portable this time). Select MiniTool Partition Wizard on launcher.
6.- Locate the destination disk on list and select 4th partition (it will be shown as GPT and unformatted). Right click and delete partition.
7.- Right click again and create partition. Select EXT4 for formatting as file system and the capacity you want. (EXT4 in my case, please check the correct filesystem on source disk for this partition)
8.- Click on apply changes (Top left of screen)
Once finished, mount the small HD on case and connect it to main and net. It will recreate all the folders on 4th partition automatically, and it will be ready to use.
Additional step: If you want to keep a copy of your OS, use HDD Raw Copy Tool again but select "FILE" as destination HDD. Stop copy after 12.000.000 sectors, as they hold the swap and OS partitions, and you will backup only the first 6Gb (it works for me with 1Tb, maybe for 2 and 3 Tb offset needs to be recalculated). You may need to repeat steps 6 and 7 when you restore the backup.
Notes: In my case, source disk was 1Tb and useful partitons to be copied were 5Gb (approx.), so I stopped the copy at 12.000.000 sectors (I don't know if mirror/swap partitions on greater HDs than 1Tb are 2Gb/489Mb each, so maybe 50.000.000 sectors are safe for all). As GPT table is on first sectors, 4th partition is defined on GPT but contents are not copied.
Here comes the problems. First of all, I mounted again the case and did a Factory reset form webUI, but it formatted 4th partition as ~900Gb. It worked, but copying something on this partition caused the device to enter in fault mode (red led). I connected the 250Gb HD to a PartedMagic machine and tried to resize/delete/make something with 4th partition, but no way. It said that the partiton cannot exceed the disk lenght, no matter which tool I used. So, back to Windows.
Please note that it is not necessary to make a factory reset from WebUI to accomplish this guide, it has been only for information.
Thats all. Hope this procedure can help someone else.