diff --git a/meta-balena-common/classes/image-balena.bbclass b/meta-balena-common/classes/image-balena.bbclass
index 54296dd84f..d41b964e4f 100644
--- a/meta-balena-common/classes/image-balena.bbclass
+++ b/meta-balena-common/classes/image-balena.bbclass
@@ -459,20 +459,19 @@ python do_image_size_check() {
     image_size_aligned = int(disk_aligned(d, os.stat(imgfile).st_size / 1024))
     available = int(disk_aligned(d, available_space(ext4file, d)))
 
-    # Calculate /boot directory size - copied to volume during HUP
-    boot_dir = os.path.join(d.getVar("IMAGE_ROOTFS"), "boot")
-    boot_size_kb = get_dir_size_kb(boot_dir)
-    boot_size_aligned = int(disk_aligned(d, boot_size_kb))
+    # mobynit init only is stored on the inactive root slot during HUP
+    boot_init = os.path.join(d.getVar("IMAGE_ROOTFS"), "boot", "init")
+    boot_init_size_kb = int(disk_aligned(d, os.path.getsize(boot_init) / 1024 if os.path.isfile(boot_init) else 0))
 
-    # Total space required = docker image + boot volume
-    total_required = image_size_aligned + boot_size_aligned
+    # Total space required = docker image + mobynit init on root slot
+    total_required = image_size_aligned + boot_init_size_kb
 
     if total_required > available:
-        bb.fatal("HUP size check failed: docker image (%d KiB) + /boot volume (%d KiB) = %d KiB exceeds available space %d KiB"
-                 % (image_size_aligned, boot_size_aligned, total_required, available))
+        bb.fatal("HUP size check failed: docker image (%d KiB) + mobynit init (%d KiB) = %d KiB exceeds available space %d KiB"
+                 % (image_size_aligned, boot_init_size_kb, total_required, available))
 
-    bb.debug(1, 'HUP size check: docker image %d KiB, /boot volume %d KiB, total %d KiB, available %d KiB'
-             % (image_size_aligned, boot_size_aligned, total_required, available))
+    bb.debug(1, 'HUP size check: docker image %d KiB, mobynit init %d KiB, total %d KiB, available %d KiB'
+             % (image_size_aligned, boot_init_size_kb, total_required, available))
 }
 
 # Equivalent to:
diff --git a/meta-balena-common/classes/image_types_balena.bbclass b/meta-balena-common/classes/image_types_balena.bbclass
index 99729e7bf6..145943d962 100644
--- a/meta-balena-common/classes/image_types_balena.bbclass
+++ b/meta-balena-common/classes/image_types_balena.bbclass
@@ -1,5 +1,7 @@
 inherit image_types
 
+require ${@os.path.join(d.getVar('BALENA_COREBASE'), 'recipes-containers/docker-disk/balena-data-partition.inc')}
+
 #
 # Create a raw image that can by written onto a storage device using dd/etcher.
 #
@@ -124,6 +126,7 @@ BALENA_BOOT_FINGERPRINT_PATH ?= "${WORKDIR}/${BALENA_FINGERPRINT_FILENAME}.${BAL
 BALENA_IMAGE_BOOTLOADER ?= "virtual/bootloader"
 BALENA_RAW_IMG_COMPRESSION ?= ""
 BALENA_DATA_FS ?= "${DEPLOY_DIR_IMAGE}/${BALENA_DATA_FS_LABEL}.img"
+BALENA_DATA_STAGING_TAR ?= "${DEPLOY_DIR_IMAGE}/${BALENA_DATA_STAGING}"
 BALENA_BOOT_FS = "${WORKDIR}/${BALENA_BOOT_FS_LABEL}.img"
 BALENA_ROOTB_FS = "${WORKDIR}/${BALENA_ROOTB_FS_LABEL}.img"
 BALENA_STATE_FS ?= "${WORKDIR}/${BALENA_STATE_FS_LABEL}.img"
@@ -180,7 +183,7 @@ IMAGE_CMD:balenaos-img () {
 
     # resin-data
     if [ -n "${BALENA_DATA_FS}" ]; then
-        BALENA_DATA_SIZE=`du -bks ${BALENA_DATA_FS} | awk '{print $1}'`
+        BALENA_DATA_SIZE=$(expr ${BALENA_DATA_PARTITION_SIZE_MB} \* 1024)
         BALENA_DATA_SIZE_ALIGNED=$(expr ${BALENA_DATA_SIZE} \+ ${BALENA_IMAGE_ALIGNMENT} \- 1)
         BALENA_DATA_SIZE_ALIGNED=$(expr ${BALENA_DATA_SIZE_ALIGNED} \- ${BALENA_DATA_SIZE_ALIGNED} \% ${BALENA_IMAGE_ALIGNMENT})
     else
@@ -331,8 +334,25 @@ IMAGE_CMD:balenaos-img () {
         bbfatal "Rootfs labeling for type '${BALENA_ROOT_FSTYPE}' has not been implemented!"
     fi
 
+    # Build resin-data.img: docker-disk is saved as a tar, we will add boot-A dir into it with all boot files.
     if [ -n "${BALENA_DATA_FS}" ]; then
-        e2label ${BALENA_DATA_FS} ${BALENA_DATA_FS_LABEL}
+        if [ ! -f "${BALENA_DATA_STAGING_TAR}" ]; then
+            bbfatal "resin-data: ${BALENA_DATA_STAGING_TAR} missing"
+        fi
+        if [ ! -d "${IMAGE_ROOTFS}/boot" ] || [ -z "$(ls -A "${IMAGE_ROOTFS}/boot" 2>/dev/null)" ]; then
+            bbfatal "resin-data: ${IMAGE_ROOTFS}/boot is empty"
+        fi
+        _balena_data_root=$(mktemp -d)
+        tar -xf "${BALENA_DATA_STAGING_TAR}" -C "${_balena_data_root}"
+        mkdir -p "${_balena_data_root}/boot-A"
+        cp -a "${IMAGE_ROOTFS}/boot/." "${_balena_data_root}/boot-A/"
+        rm -f "${BALENA_DATA_FS}"
+        dd if=/dev/zero of="${BALENA_DATA_FS}" bs=1M count=0 seek="${BALENA_DATA_PARTITION_SIZE_MB}"
+        mkfs.ext4 -E lazy_itable_init=0,lazy_journal_init=0 -T default -b ${BALENA_DATA_FS_BLOCK_SIZE} -i 8192 -d "${_balena_data_root}" -F "${BALENA_DATA_FS}" || \
+            bbfatal "resin-data: mkfs.ext4 failed (try increasing BALENA_DATA_PARTITION_SIZE_MB)"
+        e2label "${BALENA_DATA_FS}" "${BALENA_DATA_FS_LABEL}"
+        rm -rf "${_balena_data_root}"
+        bbnote "Built ${BALENA_DATA_FS} from ${BALENA_DATA_STAGING_TAR} and boot-A"
     fi
 
     #
diff --git a/meta-balena-common/recipes-bsp/grub/grub-conf/grub.cfg_internal_template b/meta-balena-common/recipes-bsp/grub/grub-conf/grub.cfg_internal_template
index 35b40d9071..447f5e81d6 100644
--- a/meta-balena-common/recipes-bsp/grub/grub-conf/grub.cfg_internal_template
+++ b/meta-balena-common/recipes-bsp/grub/grub-conf/grub.cfg_internal_template
@@ -39,29 +39,44 @@ function get_root_uuid {
  done
 }
 
-menuentry 'boot'{
-if [ ${bootcount} = 2 ] ; then
- if [ ${resin_root_part} = 2 ] ; then
-  get_root_uuid "resin-rootB"
- else
-  get_root_uuid "resin-rootA"
- fi
-else
- if [ ${resin_root_part} = 2 ] ; then
-  get_root_uuid "resin-rootA"
+function select_root_slot_and_boot_dir {
+ if [ ${bootcount} = 2 ] ; then
+  if [ ${resin_root_part} = 2 ] ; then
+   set root_slot_label=resin-rootB
+   set data_boot_dir=/boot-B
+  else
+   set root_slot_label=resin-rootA
+   set data_boot_dir=/boot-A
+  fi
  else
-  get_root_uuid "resin-rootB"
+  if [ ${resin_root_part} = 2 ] ; then
+   set root_slot_label=resin-rootA
+   set data_boot_dir=/boot-A
+  else
+   set root_slot_label=resin-rootB
+   set data_boot_dir=/boot-B
+  fi
  fi
-fi
-linux /boot/@@KERNEL_IMAGETYPE@@ root=UUID=${root_uuid} @@KERNEL_CMDLINE@@ ${extra_os_cmdline} ${extra_os_firmware_class_path}
+}
+
+menuentry 'boot' {
+ select_root_slot_and_boot_dir
+ get_root_uuid ${root_slot_label}
+ set root_slot_uuid=${root_uuid}
+ get_root_uuid "resin-data"
+ linux ${data_boot_dir}/@@KERNEL_IMAGETYPE@@ root=UUID=${root_slot_uuid} @@KERNEL_CMDLINE@@ ${extra_os_cmdline} ${extra_os_firmware_class_path}
 }
 
 menuentry 'manualfallbackA' {
-  get_root_uuid "resin-rootA"
-  linux /boot/@@KERNEL_IMAGETYPE@@ root=UUID=${root_uuid} @@KERNEL_CMDLINE@@ ${extra_os_cmdline} ${extra_os_firmware_class_path}
+ get_root_uuid "resin-rootA"
+ set root_slot_uuid=${root_uuid}
+ get_root_uuid "resin-data"
+ linux /boot-A/@@KERNEL_IMAGETYPE@@ root=UUID=${root_slot_uuid} @@KERNEL_CMDLINE@@ ${extra_os_cmdline} ${extra_os_firmware_class_path}
 }
 
 menuentry 'manualfallbackB' {
-  get_root_uuid "resin-rootB"
-  linux /boot/@@KERNEL_IMAGETYPE@@ root=UUID=${root_uuid} @@KERNEL_CMDLINE@@ ${extra_os_cmdline} ${extra_os_firmware_class_path}
+ get_root_uuid "resin-rootB"
+ set root_slot_uuid=${root_uuid}
+ get_root_uuid "resin-data"
+ linux /boot-B/@@KERNEL_IMAGETYPE@@ root=UUID=${root_slot_uuid} @@KERNEL_CMDLINE@@ ${extra_os_cmdline} ${extra_os_firmware_class_path}
 }
diff --git a/meta-balena-common/recipes-containers/docker-disk/balena-data-partition.inc b/meta-balena-common/recipes-containers/docker-disk/balena-data-partition.inc
new file mode 100644
index 0000000000..3ed226d6ec
--- /dev/null
+++ b/meta-balena-common/recipes-containers/docker-disk/balena-data-partition.inc
@@ -0,0 +1,4 @@
+# Shared resin-data partition settings (docker-disk seed + balenaos-img mkfs).
+BALENA_DATA_PARTITION_SIZE_MB ?= "256"
+BALENA_DATA_FS_BLOCK_SIZE ?= "4k"
+BALENA_DATA_STAGING ?= "resin-data-staging.tar"
diff --git a/meta-balena-common/recipes-containers/docker-disk/docker-disk.bb b/meta-balena-common/recipes-containers/docker-disk/docker-disk.bb
index 9795fe37f8..8a12d8c769 100644
--- a/meta-balena-common/recipes-containers/docker-disk/docker-disk.bb
+++ b/meta-balena-common/recipes-containers/docker-disk/docker-disk.bb
@@ -12,11 +12,9 @@ B = "${S}/build"
 
 inherit deploy
 require docker-disk.inc
+require balena-data-partition.inc
 require recipes-containers/balena-supervisor/balena-supervisor.inc
 
-PARTITION_SIZE ?= "192"
-FS_BLOCK_SIZE ?= "4k"
-
 PV = "${HOSTOS_VERSION}"
 
 RDEPENDS:${PN} = "balena"
@@ -29,10 +27,6 @@ do_compile () {
 	if [ -z "${SUPERVISOR_FLEET}" ] || [ -z "${SUPERVISOR_VERSION}" ]; then
 		bbfatal "docker-disk: SUPERVISOR_FLEET and/or SUPERVISOR_VERSION not set."
 	fi
-	if [ -z "${PARTITION_SIZE}" ]; then
-		bbfatal "docker-disk: PARTITION_SIZE needs to have a value (megabytes)."
-	fi
-
 	# At this point we really need internet connectivity for building the
 	# docker image
 	if [ "x${@connected(d)}" != "xyes" ]; then
@@ -65,8 +59,7 @@ do_compile () {
 		-e HOSTAPP_PLATFORM="${HOSTAPP_PLATFORM}" \
 		-e BALENA_API_ENV="${BALENA_API_ENV}" \
 		-e BALENA_API_TOKEN="${_token}" \
-		-e PARTITION_SIZE="${PARTITION_SIZE}" \
-		-e FS_BLOCK_SIZE="${FS_BLOCK_SIZE}" \
+		-e BALENA_DATA_STAGING="${BALENA_DATA_STAGING}" \
 		-v /sys/fs/cgroup:/sys/fs/cgroup:ro -v ${B}:/build \
 		--name ${_container_name} ${_image_name}
 	$DOCKER rmi -f ${_image_name}
@@ -82,7 +75,7 @@ do_install () {
 FILES:${PN} += "/etc/hostapp-extensions.conf"
 
 do_deploy () {
-	install -m 644 ${B}/resin-data.img ${DEPLOYDIR}/resin-data.img
+	install -m 644 ${B}/${BALENA_DATA_STAGING} ${DEPLOYDIR}/${BALENA_DATA_STAGING}
 }
 addtask deploy before do_package after do_install
 
diff --git a/meta-balena-common/recipes-containers/docker-disk/files/entry.sh b/meta-balena-common/recipes-containers/docker-disk/files/entry.sh
index 0f130bc43e..9c103c8b67 100644
--- a/meta-balena-common/recipes-containers/docker-disk/files/entry.sh
+++ b/meta-balena-common/recipes-containers/docker-disk/files/entry.sh
@@ -6,7 +6,6 @@ set -o nounset
 DOCKER_TIMEOUT=20 # Wait 20 seconds for docker to start
 DATA_VOLUME=/resin-data
 BUILD=/build
-PARTITION_SIZE=${PARTITION_SIZE:-1024}
 DOCKER_HOST=unix:///var/run/docker.sock
 
 finish() {
@@ -74,8 +73,4 @@ kill -TERM "$(cat /var/run/docker.pid)"
 # don't let wait() error out and crash the build if the docker daemon has already been stopped
 wait "$(cat /var/run/docker.pid)" || true
 
-# Export the final data filesystem
-dd if=/dev/zero of=${BUILD}/resin-data.img bs=1M count=0 seek="${PARTITION_SIZE}"
-
-# Usage type default, block size 4k defined in recipe. See https://github.com/tytso/e2fsprogs/issues/50
-mkfs.ext4 -E lazy_itable_init=0,lazy_journal_init=0 -T default -b ${FS_BLOCK_SIZE}  -i 8192 -d ${DATA_VOLUME} -F ${BUILD}/resin-data.img
+tar -cf ${BUILD}/${BALENA_DATA_STAGING} -C ${DATA_VOLUME} .
diff --git a/meta-balena-common/recipes-containers/hostapp-update/files/hostapp-update b/meta-balena-common/recipes-containers/hostapp-update/files/hostapp-update
index 9aa505c071..b6b1bb98a9 100644
--- a/meta-balena-common/recipes-containers/hostapp-update/files/hostapp-update
+++ b/meta-balena-common/recipes-containers/hostapp-update/files/hostapp-update
@@ -23,6 +23,77 @@ ERROR() {
 	fi
 }
 
+# Map the inactive root slot to resin-data boot dir (boot-A / boot-B).
+data_boot_slot() {
+	if [ ! -e /dev/disk/by-state/inactive ] || [ ! -e /dev/disk/by-state/resin-rootA ]; then
+		return 1
+	fi
+	inactive_dev=$(readlink -f /dev/disk/by-state/inactive)
+	roota_dev=$(readlink -f /dev/disk/by-state/resin-rootA)
+	if [ "$inactive_dev" = "$roota_dev" ]; then
+		echo "boot-A"
+	else
+		echo "boot-B"
+	fi
+}
+
+# Stage hostapp /boot on resin-data boot-{A|B} for GRUB
+stage_boot_to_data_partition() {
+	container_id="$1"
+	slot=""
+
+	if ! mountpoint -q /mnt/data 2>/dev/null; then
+		INFO "Skipping data-partition boot staging (/mnt/data not mounted)"
+		return 0
+	fi
+
+	if ! slot=$(data_boot_slot); then
+		INFO "Skipping data-partition boot staging (inactive root slot unknown)"
+		return 0
+	fi
+
+	data_boot_dir="/mnt/data/${slot}"
+	data_boot_new="${data_boot_dir}.new"
+
+	rm -rf "$data_boot_new"
+	mkdir -p "$data_boot_new"
+	if ! _out=$(balena cp "${container_id}:/boot/." "${data_boot_new}/" 2>&1); then
+		ERROR "Failed to copy boot files to data partition: ${_out}"
+		exit 1
+	fi
+	if [ -z "$(ls -A "$data_boot_new" 2>/dev/null)" ]; then
+		ERROR "Hostapp /boot is empty"
+		exit 1
+	fi
+	sync -f /mnt/data
+
+	rm -rf "${data_boot_dir}.old" 2>/dev/null || true
+	if [ -d "$data_boot_dir" ]; then
+		mv "$data_boot_dir" "${data_boot_dir}.old"
+	fi
+	mv -T "$data_boot_new" "$data_boot_dir"
+	sync -f /mnt/data
+	rm -rf "${data_boot_dir}.old" 2>/dev/null || true
+
+	INFO "Staged boot payload to ${data_boot_dir}/"
+}
+
+# Root-slot boot dir holds mobynit init only
+install_hostapp_init() {
+	container_id="$1"
+	hostapp_boot="$2"
+
+	mkdir -p "$hostapp_boot"
+	if ! _out=$(balena cp "${container_id}:/boot/init" "${hostapp_boot}/" 2>&1); then
+		ERROR "Failed to copy mobynit init: ${_out}"
+		exit 1
+	fi
+	if [ ! -x "${hostapp_boot}/init" ]; then
+		ERROR "Hostapp /boot/init missing or not executable"
+		exit 1
+	fi
+}
+
 run_current_hooks_and_recover () {
 	if [ "$hooks_rollback" = 1 ]; then
 		# Run the current ones to cleanup the system.
@@ -124,13 +195,13 @@ elif [ "$remote_image" != "" ]; then
 	_out="$(balena pull "$HOSTAPP_IMAGE" 2>&1)"
 	INFO "${_out}"
 fi
-CONTAINER_ID=$(balena create --runtime="bare" --volume=/boot "$HOSTAPP_IMAGE" /bin/sh)
-BOOTSTRAP=$(balena inspect -f "{{range .Mounts}}{{.Destination}} {{.Source}}{{end}}" "$CONTAINER_ID" | awk '$1 == "/boot" { print $2 }' | head -n1)
+CONTAINER_ID=$(balena create --runtime="bare" "$HOSTAPP_IMAGE" /bin/sh)
+
+stage_boot_to_data_partition "$CONTAINER_ID"
 
-# Create boot entry
 rm -rf "$SYSROOT/hostapps/.new"
 mkdir -p "$SYSROOT/hostapps/.new"
-ln -sr "$BOOTSTRAP" "$SYSROOT/hostapps/.new/boot"
+install_hostapp_init "$CONTAINER_ID" "$SYSROOT/hostapps/.new/boot"
 sync -f "$SYSROOT"
 mv -T "$SYSROOT/hostapps/.new" "$SYSROOT/hostapps/$CONTAINER_ID"
 sync -f "$SYSROOT"