If ITE2 NAS user encounter single hard drive damage (system status: unsafe or abnormal) under RAID 1 type. They can rebuild data by Add hot spare method.
First, you have to replace damaged hard drive with a new one.
For how to replace the hard drive, please refer to Replace damaged HDD in Windows 10 NAS.
Add hot spare
Once you have replaced the hard drive, please go to PDM [Settings> HDD Management> Space Management and click [Add hot spare].
Then, select the new hard drive you want to add hot spare, and press [OK].
You can see the system status display [Rebuild]. If you did not see the updated status, press [Rescan Hardware Devices] to update the newest status.
After finish rebuilding, you can see the status has updated to [Good], and the information about the damaged hard drive was removed.