This is a mystery to me.
I have been fiddling with the MBWEII Blue Rings (currently 2x500 RAID1) because I am trying to upgrade it to 2x2T RAID1 but I want to understand what I am doing, instead of just copying commands from my screen. Instead of using the dd commands or the rsync, I have followed the "safe way", and I must admit I have come to a point where I have my new 2TB disk ready to be filled with my things and ready for mirroring on the second one.
However, there is something that, no matter what I do, I cannot understand.
When I was trying to do some experiments in order to find the safest, quickest, best way to copy my data from the old disks to the new ones, I tried this: I took out one of the original disks, I replaced it with the new one, I had the Mybook rebuild the array and everything went fine. I ended up with one original 500 GB disk and a new 2TB disk with the sdb4 mirrored partition of about 490 GB, and the rest unallocated. So far so good.
Then I did something I was expecting to succeed, but it did not. I took out the new disk, I connected with a Linux PC and I enlarged the sdb4 partition to fill it completely. I restored the FD type partition and I put it, alone, in the MBWE. To my surprise, it didn't boot at all. Not that it booted giving me a partition size error, a "not recognized" partition or any other kind of error. It didn't boot at all.
Then, intrigued, I took one of the two original 500 GB disks, I put it in the linux PC, too, I changed the sdb4 partition type from FD to 83, I copied my files (only copied, I didn't write a thing on that disk), I changed the partition type back to FD, I put it (alone) in the MyBook and… surprise: it didn't boot!!!
It seems that, whatever operation which implies to write to the disk, as simple as it can be (just changing a partition type and then back) from gparted, then that disk won't boot anymore even if, apparently, nothing has changed in the partition structure, position, type, size, whatever. Obviously something changes, just I cannot understand what! I was thinking about the UUID, but I don't know exactly what it is and where it is stored… Furthermore, all the operations described to unbrick the MBWE which make use of the dd commands do not ever change the UUID… Could it be because the dd does not change the UUID and gparted does? Or the UUID is not involved at all and it is something else I am missing?
Understanding this is particularly important because I would like to be able to use the EARS (advanced format) disks at their best, so probably I'd better take care of partitioning from within gparted, but first I must understand the trick!
Thanks to all those who will be so kind to help me understand a little better! :-)