uefi - Installing Ubuntu 16.10 64BIT on External HD in Legancy Mode ("Reserved BIOS boot area" issue) - Ask Ubuntu

i beginner , want try ubuntu first time.

i have lenovo y700 laptop uefi (access uefi "novo" button)

i want install ubuntu on external hd (wd passport 1tb), without influencing system boot, uefi , internal drive (with win10 on it).

now, know many users had problem after installing ubuntu on external hd on pc pre-installed windows in efi mode.

as understand, prevent changes in uefi, 1 of solutions install ubuntu in legancy mode. don't mind change between legancy mode , uefi anytime need use either win10 or ubuntu.

so, used rufus image ubuntu-16.10-desktop-amd64.iso make bootable ubuntu installation usb stick first. set mbr partition scheme bios or uefi in fat32 file system.

then boot ubuntu in legancy mode, connected network , start installation progress.

1. i've chosen boot loader installed in dev/sdd (my dedicated external drive).
2. i created 2 partitions on sdd drive: swap partition , main ext4 partition. there big ntfs partition don't want use ubuntu.

when press install now, instead regular "write changes disks?" window confirm changes , start installation, following window:

go menu , correct problem?

the partition table format in use on disks requires create separate partition boot loader code. partition should marked use “reserved bios boot area” , should @ least 1 mb in size. note not same partition mounted on /boot. if not go partitioning menu , correct error, bootloader installation may fail later, although may still possible install boot loader partition.

there 2 options:

1. go back - create "reserved bios boot area" partition.
2. continue

which of these need choose, in order not make changes internal drive, uefi settings , not harm win10 boot?

thanks!