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ROOT Partition Settings

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Define the ZFS Pool Name

This is the default name to be assigned to the ZFS pool. Some people really can't sleep well at night if their ZFS pools don't have the perfect name.

# Define Pool Names - can be set to whatever you like.
# Short hostname is default, this is like "rpool" in the previous methods.
root_pool_name: "{{ host_name }}"

Based on the name above then:

  • User data will be stored in ZFS Dataset: {host_name}/ROOT/home
  • Operating System is within ZFS Dataset: {host_name}/ROOT/ubuntu

NOTE: The Operating System dataset has automatically snapshots created when apt or dpkg installs or removes packages. This allows the OS to be rolled back to previous snapshots without impacting user data.

Root Partition Size

  • By default the root partition size will decided by ZFS at pool creation to use the largest possible value.

    • If devices of different size are used then the size of the root pool will be limited to the space left on the smallest device.
    • For example: if the smallest device has 250GiB for the root pool, then all devices that are part of the root pool will only contribute 250Gib towards the pool. All of these devices (VDEVs in ZFS terms) must be the same.
      • All remaining space not used will remain unallocated. If in the future when the smallest device is replaced. Then partition sizes can be adjusted and the ZFS pool can be expanded to use the additional space.

  • You can specify a specific partition size for the root pool on each device in the storage pool. This is useful if you want a standard size partitions on each computer.

  • Or you can specify how much space NOT to use leaving a specific amount of unallocated space for some other use.

    ###############################################################################
# The root pool by default will consume all remaining disk space on the devices
# limited by the free space of the smallest device specified.  For example a
# mirror between a 512GB and 256GB device cannot be larger than the capacity of
# the smaller device.

# If you wish to limit the root pool size leaving unused space, you can define
# that here.  Specify how much space to allocate or NOT allocate per root pool
# partition per device.

# Examples:
# "+256G" will create partitions 256Gib in size
# "-200M" will use all available space, minus 200Mib
# "0" (zero) use all available space
root_partition_size: "0"

  • If you decided to have unallocated space left, the remaining storage space will be after the last partition created. This simplifies making additional partitions later or expanding expanding partitions later.

Prompt for ZFS Passphrase

ZFS Native Encryption is enabled by simply specifiying a passphrase to use for encryption. If you plan to always use encryption then set this to true. Ansible will prompt you for the passphrase if you forget to provide it via the command line. If this is false and no passphrase is provided via the command line to ansible, then ZFS native encryption will not be used.

# Prompt for Native ZFS Encryption Passphrase.  if true, then prompt for
# passphrase if not provided.
prompt_for_zfs_passphrase: false

ZFS Specific Adjustable Settings

Define ZFS Root Pool Type Rules:

  • Any EVEN number of devices (2, 4, 6, 8..), specified to be a mirror will be a mirrored vdev pair (which is awesome!)

    • This is the recommended way to configure ZFS with many devices instead of using raidz.

    • This is higher performance and much fastest recovery from a single disk failure.

    • This topology is not available from Ubuntu installer or with the OpenZFS HowTo method.

    • If you don't want this, then use raidz or raidz2 type

  • Any ODD number of devices should be a raidz or raidz2 type

    • A raidz2 can be tried with 4 or more devices.

  • You can add additional entries to meet your requirements. Anything not defined below will be be treated as raidz1 pool.

    # Define the root pool type based on number of devices.
#  - If you want 3 devices to be a 3 way mirror change it, etc.
#  - If even number 2,4,6,8, etc of type mirror, then mirrored vdevs will be used.
#  - -  This is higher performance with redundancy and much faster resilver times
#  - -  than using any type of raidz.
#  - Raidz will be the default if something below is not defined.
#  - NOTE: A raidz2 requires 4 or more devices.
set_root_pool_type:
  1: ""
  2: "mirror"
  3: "raidz"
  4: "mirror"
  5: "raidz"
  6: "mirror"
  default: "raidz"

Ashift Value

The ZFS ashift value for modern devices with 512 byte or 4K sector size should be 12. Some flash devices could see better performance with 13 as internally they might be 8K devices. Many devices simply lie about what they truly are due compatibility reasons.

# Define ZFS ashift value to use
zfs_rpool_ashift: 12
  • If ashift is too high, you lose a bit of space if you have a massive amount of very small files. If it’s too low, you get write amplification and performance degradation.

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