Skip to main content

Partition Size Recommendations

This document provides recommendations for partition sizes in your Trident Host Configuration. These sizes are used by Trident to manage the operating system installation and update. The recommended sizes are based on typical use cases and may need to be adjusted based on specific requirements.

note

For A/B volume pairs, i.e. partitions that are configured to be updated with A/B updates, like root, the sizes of each (root-a and root-b) must be the same.

The recommendations below are specific to Azure Linux unless otherwise noted.

ESP​

The EFI System Partition (ESP) is used for storing boot loaders and related files.

For a single boot system, 512MB is recommended.

For multiboot systems, each operating system should be accounted for. Azure Linux should have at least 512MB. For other operating systems, be aware of their recommendations.

storage:
  disks:
    - id: os
      partitions:
        - id: esp
          type: esp
          size: 512M

Root​

The root partition size depends on the operating system being installed. The minimum recommended size for root is 4GB.

note

Using the minimal size does not leave much room for additional packages or container images. Consider your use case and adjust the size accordingly.

storage:
  disks:
    - id: os
      partitions:
        - id: root
          size: 4G

dm-verity Hash (root or usr)​

When configuring a dm-verity system, you need to allocate space for the dm-verity hash tree. The size of the hash tree depends on the size of the partition being protected and the block size used for hashing.

https://wiki.archlinux.org/title/Dm-verity#Partitioning suggests creating a hash partition that is 8-10% of the size of the partition being protected.

storage:
  disks:
    - id: os
      partitions:
        - id: root-hash
          size: 256M

Trident State​

By default, Trident stores its state in /var/lib/trident. This includes logs and other persistent state that Trident needs to operate. This path can be customized, but because it is used to store state that persists across updates, it must not be placed on an A/B volume pair.

Regardless of the location, the recommendation is to allocate at least 256MB for that partition.

storage:
  disks:
    - id: os
      partitions:
        - id: trident
          size: 256M

Boot​

The boot partition (/boot) is used for storing the kernel and initramfs files.

/boot must be a separate partition when creating COSI images configured with:

The boot partition size should be at least 150MB to accommodate the updated GRUB configuration generated by Image Customizer during verity customization. This prevents space exhaustion when writing or updating grub.cfg.

storage:
  disks:
    - id: os
      partitions:
        - id: boot
          type: xbootldr
          size: 150M

Other Partitions​

There are a lot of scenarios where you might want to define additional partitions. Customers often create partitions to carve out dedicated spaces for subtrees, e.g. /var.

These partitions should be sized according to your specific needs and use cases.