Maintenance Mode indicates that the system is unable to detect the hard drives, the hard drives cannot be correctly mounted, or the disk is experiencing corruption.

If the hard drives have no physical issues this can be fixed by repairing the file system:
Note: this command will reboot the system.

diagnose system fsck harddisk
This operation will check and repair the file system, then reboot the system.
Do you want to continue? (y/n)y

If the file system repair does not fix the issue, formatting the log disk may be required:

execute format disk-ext4 <-- Format log disk into ext4 file system.
This operation will format hard disk with ext4 file system.
Do you want to continue? (y/n)y

This method will cause all logs to be lost as the hard drive(s) will be formatted.