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Rootfs A/B Redundancy

Complete guide to Rootfs A/B redundancy mechanism on NVIDIA Jetson devices.

Overview​

Rootfs A/B Redundancy provides:

  • ✅ System Redundancy: Two independent rootfs partitions (A and B)
  • ✅ Automatic Fallback: Switches to backup on boot failure
  • ✅ Seamless Updates: Update without affecting current operation
  • ✅ Disaster Recovery: Automatic recovery on failure

Root File System Redundancy​

Jetson Linux provides support for root file system redundancy on NVIDIA® Jetson Orin series.

It uses two root file systems:

  • Rootfs A: Stored in the usual file system partition (APP)
  • Rootfs B: Stored in a new partition (APP_b), located after APP on the disk

Rootfs A/B Partition Layout

Each rootfs is independent and occupies a slot: "slot A" or "slot B".

  • Bootloader A always boots with rootfs A
  • Bootloader B always boots with rootfs B

Bootloader and Rootfs

  • Boot ROM retrieves the target slot number from either the BR-BCT or Scratch Registers.
  • Load the corresponding Bootloader stages and boot to the assigned rootfs partition.

Bootloader and Rootfs

Implementation Guide​

Step 1: Prepare Host​

Prepare the following:

  • ✅ X86 Host PC with Ubuntu 22.04 or later
  • ✅ Disk Space: At least 256 GiB
  • ⚠️ Do not use VM - Use physical PC
  • ✅ USB Cable: Type-A to Type-C
  • ✅ Jetson Device: AFE-R750 example

Host Preparation

USB Connection

Step 2: Prepare Image on Host​

Download Image:

Important Notes:

  • ❌ Do NOT use root# or mouse to extract
  • ✅ Download the same JetPack image version as on Jetson device

Step 3: Install Pre-requisites​

sudo usermod -aG dialout $USER
sudo apt update
sudo ./Linux_for_Tegra/tools/l4t_flash_prerequisites.sh
sudo reboot

Step 4: Get Storage Parameters​

sudo fdisk -l /dev/nvme0n1

Example:

  • Storage_real_size: 119.2 GB
  • Sectors_number: 250069680

Bootloader and Rootfs

Step 5: Modify Config File​

sudo gedit Linux_for_Tegra/tools/kernel_flash/flash_l4t_t234_nvme_rootfs_ab.xml

Set num_sectors to Sectors_number.

Bootloader and Rootfs

Step 6: Put Device in Recovery Mode​

  1. Shutdown Jetson device

  2. Connect USB to FLASH port Power Off and Connect

  3. Open bottom cover Recovery Setup

  4. Set RST_RCOVY pin 2 to ON

  5. Press power button Recovery Pins

Step 7: Verify Connection​

On Host, open terminal and execute:

lsusb

Verify that AFE-R750 is detected in recovery mode.

Connection Verification

Step 8: Flash Image with Redundancy​

cd Linux_for_Tegra

AGX Orin eMMC:

sudo ROOTFS_AB=1 ROOTFS_RETRY_COUNT_MAX=1 ./flash.sh jetson-agx-orin-devkit mmcblk0p1

AGX Orin NVMe: Adjust the -S parameter based on the SSD volume

sudo ROOTFS_AB=1 ROOTFS_RETRY_COUNT_MAX=1 ./tools/kernel_flash/l4t_initrd_flash.sh \
  --external-device nvme0n1p1 \
  -c tools/kernel_flash/flash_l4t_t234_nvme_rootfs_ab.xml \
  -p "-c bootloader/generic/cfg/flash_t234_qspi.xml" \
  -S '<58GiB>' \
  --showlogs \
  --network usb0 \
  jetson-agx-orin-devkit \
  nvme0n1p1

Orin NX NVMe:

sudo ROOTFS_AB=1 ROOTFS_RETRY_COUNT_MAX=1 ./tools/kernel_flash/l4t_initrd_flash.sh \
  --external-device nvme0n1p1 \
  -c tools/kernel_flash/flash_l4t_t234_nvme_rootfs_ab.xml \
  -p "-c bootloader/generic/cfg/flash_t234_qspi.xml" \
  -S `<58GiB>` \
  --showlogs \
  --network usb0 \
  jetson-orin-nano-devkit \
  internal

Note: Half of Storage_real_size (integer only).

  • 119.2 / 2 = 58.6 → 58 GiB

Step 8: Check Redundancy Function​

sudo nvbootctrl -t rootfs dump-slots-info
sudo nvbootctrl -t rootfs set-active-boot-slot `1`
sudo reboot

After reboot, check slot info again - Rootfs has changed.

References​

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