After installing a new hard drive into a server for the purpose of mirroring the data from the first drive to the second one, the server displays an "operating system not found" error. Which of the fo

Replacing the second drive with a hot-swappable one does not address the issue of the server attempting to boot from the incorrect drive.

Adding a new hard drive can alter the system's boot order, causing it to attempt to boot from the newly installed, empty drive; changing the boot order in the BIOS/UEFI to explicitly select the original drive ensures the system loads the operating system from the correct disk.

Making the second disk active is an operating system-level task performed after booting, and it would not resolve the 'operating system not found' error, as the system cannot boot to an OS to run disk management.

Rebuilding a RAID array is premature because the immediate problem is the inability to boot the operating system from the original drive, which is typically a pre-RAID configuration issue in this context.