grub on /dev/sda

preseed.cfg

@@ -87,7 +87,8 @@ d-i pkgsel/upgrade select full-upgrade
 popularity-contest popularity-contest/participate boolean false
 d-i grub-installer/only_debian boolean true
 d-i grub-installer/with_other_os boolean true
-d-i grub-installer/bootdev  string default
+#d-i grub-installer/bootdev  string default
+d-i grub-installer/bootdev string /dev/sda
 d-i debian-installer/add-kernel-opts string console=tty0 console=ttyS1,115200n8 ipv6.disable=1
 d-i finish-install/keep-consoles boolean true
 d-i finish-install/reboot_in_progress note