Index: usr.sbin/bsdinstall/bsdinstall.8
===================================================================
--- usr.sbin/bsdinstall/bsdinstall.8
+++ usr.sbin/bsdinstall/bsdinstall.8
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 21, 2019
+.Dd December 30, 2019
 .Dt BSDINSTALL 8
 .Os
 .Sh NAME
@@ -314,6 +314,12 @@
 Name for the pool containing the base system.
 Default:
 .Dq zroot
+.It Ev ZFSBOOT_ZROOT_POOL_NAME
+Size for the pool containing the base system.
+If set to anything else then MAX or an empty string, this value is passed
+to gpart as partition size.
+Default:
+.Dq MAX
 .It Ev ZFSBOOT_POOL_CREATE_OPTIONS
 Options to be used when creating the base system's pool.
 Each option must be followed by the -O flag to be taken into consideration
Index: usr.sbin/bsdinstall/scripts/zfsboot
===================================================================
--- usr.sbin/bsdinstall/scripts/zfsboot
+++ usr.sbin/bsdinstall/scripts/zfsboot
@@ -45,6 +45,13 @@
 : ${ZFSBOOT_POOL_NAME:=zroot}
 
 #
+# How much space to allocate for the zroot partition
+#       MAX means use all the leftover space
+# NOTE: Value passed to gpart(8); which supports SI unit suffixes.
+#
+: ${ZFSBOOT_ZROOT_POOL_SIZE:=MAX}
+
+#
 # Default options to use when creating zroot pool
 #
 : ${ZFSBOOT_POOL_CREATE_OPTIONS:=-O compress=lz4 -O atime=off}
@@ -262,6 +269,7 @@
 msg_invalid_disk_argument="Invalid disk argument \`%s'"
 msg_invalid_index_argument="Invalid index argument \`%s'"
 msg_invalid_swap_size="Invalid swap size \`%s'"
+msg_invalid_zroot_pool_size="Invalid zroot pool size \`%s'"
 msg_invalid_virtual_device_type="Invalid Virtual Device type \`%s'"
 msg_last_chance_are_you_sure="Last Chance! Are you sure you want to destroy\nthe current contents of the following disks:\n\n   %s"
 msg_last_chance_are_you_sure_color='\\ZrLast Chance!\\ZR Are you \\Z1sure\\Zn you want to \\Zr\\Z1destroy\\Zn\nthe current contents of the following disks:\n\n   %s'
@@ -281,11 +289,15 @@
 msg_partition_scheme="Partition Scheme"
 msg_partition_scheme_help="Select partitioning scheme. GPT is recommended."
 msg_please_enter_a_name_for_your_zpool="Please enter a name for your zpool:"
+msg_please_enter_amount_of_zroot_pool_space="Please enter amount of zroot pool space (SI-Unit suffixes\nrecommended; e.g., \`2g' for 2 Gigabytes):"
 msg_please_enter_amount_of_swap_space="Please enter amount of swap space (SI-Unit suffixes\nrecommended; e.g., \`2g' for 2 Gigabytes):"
 msg_please_select_one_or_more_disks="Please select one or more disks to create a zpool:"
 msg_pool_name="Pool Name"
 msg_pool_name_cannot_be_empty="Pool name cannot be empty."
 msg_pool_name_help="Customize the name of the zpool to be created (Required)"
+msg_zroot_pool_size="ZROOT pool Size"
+msg_zroot_pool_size_help="Customize how much space is allocated for the zroot pool"
+msg_zroot_pool_toosmall="The selected pool size (%s) is to small. Please enter a value greater than 100MB or enter MAX for using full remainder"
 msg_pool_type_disks="Pool Type/Disks:"
 msg_pool_type_disks_help="Choose type of ZFS Virtual Device and disks to use (Required)"
 msg_processing_selection="Processing selection..."
@@ -354,6 +366,9 @@
 		                        '$msg_disk_info_help'
 		'N $msg_pool_name'      '$ZFSBOOT_POOL_NAME'
 		                        '$msg_pool_name_help'
+		'Z $msg_zroot_pool_size'
+					'$ZFSBOOT_ZROOT_POOL_SIZE'
+		                        '$msg_zroot_pool_size_help'
 		'4 $msg_force_4k_sectors'
 		                        '$force4k'
 		                        '$msg_force_4k_sectors_help'
@@ -734,7 +749,8 @@
 # so we can have some real swap. This also provides wiggle room incase your
 # replacement drivers do not have the exact same sector counts.
 #
-# NOTE: $swapsize and $bootsize should be defined by the calling function.
+# NOTE: $swapsize and $zrootsize, $bootsize should be defined by the calling 
+#       function.
 # NOTE: Sets $bootpart and $targetpart for the calling function.
 #
 zfs_create_diskpart()
@@ -929,12 +945,20 @@
 		#
 		# 4. Add freebsd-zfs partition labeled `zfs#' for zroot
 		#
-		f_eval_catch $funcname gpart "$GPART_ADD_ALIGN_LABEL" \
-		             "$align_big" zfs$index freebsd-zfs $disk ||
-		             return $FAILURE
+		if [ x"$zrootsize"x = xx -o x"$zrootsize"x = x"MAX"x]; then
+			f_eval_catch $funcname gpart "$GPART_ADD_ALIGN_LABEL" \
+			             "$align_big" zfstest$index freebsd-zfs $disk ||
+			             return $FAILURE
+		else
+			f_eval_catch $funcname gpart \
+				     "$GPART_ADD_ALIGN_LABEL_WITH_SIZE" \
+			             "$align_big" zfstest$index freebsd-zfs \
+				     ${zrootsize}b $disk ||
+			             return $FAILURE
+                fi
 		f_eval_catch -d $funcname zpool "$ZPOOL_LABELCLEAR_F" \
 		                /dev/$disk$targetpart
-		;;
+		;; # END GPT
 
 	MBR) f_dprintf "$funcname: Creating MBR layout..."
 		#
@@ -1014,7 +1038,7 @@
 		f_eval_catch $funcname dd "$DD_WITH_OPTIONS" \
 		             /boot/zfsboot /dev/${disk}s1 count=1 ||
 		             return $FAILURE
-		;;
+		;; # END MBR
 
 	esac # $ZFSBOOT_PARTITION_SCHEME
 
@@ -1675,6 +1699,33 @@
 			"$msg_please_enter_a_name_for_your_zpool" \
 			"$ZFSBOOT_POOL_NAME" &&
 			ZFSBOOT_POOL_NAME="$input"
+		;;
+	?" $msg_zroot_pool_size")
+		# Prompt the user to input/change the zroot pool size 
+		while :; do
+		    f_dialog_input input \
+			    "$msg_please_enter_amount_of_zroot_space" \
+			    "$ZFSBOOT_ZROOT_POOL_SIZE" &&
+			    ZFSBOOT_ZROOT_POOL_SIZE="$input"
+		    if [ $ZFSBOOT_ZROOT_POOL_SIZE = "MAX" ]; then
+			zrootsize = "MAX"
+			break;
+	            fi
+		    if f_expand_number "$ZFSBOOT_ZROOT_POOL_SIZE" zrootsize
+		    then
+			if [ $zrootsize -ne 0 -a $zrootsize -lt 104857600 ]; then
+			    f_show_err "$msg_zroot_pool_toosmall" \
+				       "$ZFSBOOT_ZROOT_POOL_SIZE"
+			    continue;
+			else
+			    break;
+			fi
+		    else
+			f_show_err "$msg_zroot_pool_invalid" \
+				   "$ZFSBOOT_ZROOT_POOL_SIZE"
+			continue;
+		    fi
+		done
 		;;
 	?" $msg_force_4k_sectors")
 		# Toggle the variable referenced both by the menu and later