Taken from Lacie’s support FAQ:
Do the swap with power on so the embedded OS knows what’s up.
У меня есть зеркало RAID 1 на Lacie 2 Big USB3. Когда я разбиваю зеркало, вытаскивая один диск, продолжая вносить изменения в оставшийся диск и, наконец, вставляя первый, диски остаются счастливо синхронизированными. Устройство, кажется, не обнаруживает, что зеркало было сломано. В руководстве только объясняются шаги, которые необходимо предпринять для замены неисправного диска на новый. Это только повторно зеркало, если диск замены новый? На что это смотрит, чтобы определить это?
Taken from Lacie’s support FAQ:
Do the swap with power on so the embedded OS knows what’s up.
I don't know this drive specifically, but most consumer-model RAID enclosures use very simple logic to determine the health of the array. Usually this is just some metadata stored in the slack space of the disks themselves.
The simple logic only triggers a RAID fault in the following conditions:
That's it. Under "normal" conditions (i.e. you use it the way you're supposed to), replacing a bad disk would trigger a rebuild because the new disk would not have the RAID signature on it.
In your case, since you removed one of the drives while the unit is powered off, none of these fault events gets triggered. When you power it back on with only one drive, the RAID metadata gets ignored (the unit operates in single drive mode). When you put the second drive back in and power it on, the enclosure sees the metadata on both disks is identical and assumes that everything is fine. There is no hashing or checksumming that takes place to determine if the disks are in sync the way a real RAID controller would.
Lucky for you, these "dumb" RAID enclosures also do not do read balancing the way a real RAID controller would either. Data is always read from one disk in the array and the other is basically a live backup, so you're not totally corrupt when you power it on. Make no mistake, though, your mirror is broken and the disk you used on another computer is screwed up. What would happen if you attempted to fail over to it is anyone's guess. The disk should be considered totally corrupt at that point even if another computer says it's fine.