I have a Synology Diskstation 414j at my home that runs RAID 5 across 3 drives. I was curious to see what Diskstation looked like on the inside, so I unscrewed the back, took out the drives, and put the drives back into the correct slots. However, I didn't slide one of the drives back in all the way so the system gave errors once I tried to boot it back up. I pushed the drive the rest of the way and rebooted the system.
After rebooting the system I saw that it recommended rebuilding the array so I attempted to do so. This was the wrong choice because unknown to me, another drive was actually failing. I'm guessing the system didn't detect this drive was failing because we don't use the Diskstation very often. We tried copying data off, but ran into bad sector errors about 100GB in.
What should I do to save the data from the drives and how can I detect a drive failure like this in the future?