Did you turned off the unit before replacing the drive?
The unit is not hot-swappable.
I have a failed drive a few weeks ago. The procedure would be:
- turned off the unit
- Replace the failed drive
- turn the unit back on
- if I remember correctly, once I log-in to the config page, it will prompt me to format the new drive
- Then I proceed to select manual rebuild
- Once the rebuild complete, only volume 1 showed up
- then I realized all the user config were gone and I have to recreate all the user accounts for individual users to access corresponding folders
Other than the user account creation, the rebuild is quite plain sailing.
My rebuild involve a 5% filled, out of a total capacity of 6TB. And it took about 36 hours. If your unit is half filled of the same capacity, it would probably took 2 weeks!!! A 90% filled unit would took about a month to rebuild. At that point, rebuild simply becomes impractical if not impossible. A back-up will make every sense.