The original RAID configuration for this system was RAID6 + hotspare. However after I added to a disk to RAID, the RAID is now RAID6 and no hotspare. My question is that, rebuild is still running and current completion is 45% (57 TB volumes in RAID6). It took a week to get this much. It is very slow and is it normal behavior? Can we stop the rebuild process?
If you stop the rebuild they are most likely going to lose data. Once the RAID is expanded it cannot be shrunk, so the only way is to add another drive in as hot spare. They have ~ 57 TB volumes in RAID 6 that needs to reconstruct, so 45% 4 days in, looking at the size and parity, sounds reasonable.