From Fedora Project Wiki

Improve the Anaconda Btrfs preset


A few small changes will make it easier to do snapshots and rollbacks on btrfs, in the near future.


  • Name: Chris Murphy
  • Email:
  • Product: Anaconda
  • Responsible WG: Workstation, KDE SIG

Current status

  • Targeted release: Fedora 33
  • Last updated: 2020-06-15
  • FESCo issue: <will be assigned by the Wrangler>
  • Tracker bug: <will be assigned by the Wrangler>
  • Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

/boot will be on btrfs. This is supported by GRUB for ~10 years, and recently in the installer. It will make snapshotting of /boot possible, to ensure parity with /usr on rollback.

Use subvolumes for the following mountpoints: /home /var/logs /var/lib/libvirt/images. This will make it possible to avoid snapshot and rollback of logs, VM images, and user home. NOTE: the design is WIP, but also is not user facing.

Prior work in this area: Revisiting How We Put Together Linux System containers/bubblewrap


One big file system? What about clean installs and using /home?
Anaconda custom partitioning will let you reuse an existing 'home' subvolume to mount at '/home', without a reformat. A new 'root' subvolume must be created for '/' however. NOTE: Subvolumes are a bit special, but act mostly like directories, including having no size.

Benefit to Fedora

Optimize the 'btrfs preset' installation for today's use cases, and prepare for additional features. A significant benefit of btrfs is it can be a nearly drop-in replacement, and not burden users with learning esoteric things.

Default features:

  • One big file system, no longer run out of space on / or /home.
  • Full data integrity checking.ƒ
  • (Rootless) Podman will use snapshots.ƒ

Available optionally now, integration in the near future:

  • cgroupsv2 IO isolation, completes the resource control picture for better system responsiveness.ƒ
  • Transparent compression, file system/directory/file level granularity.ƒ
  • Snapshots and rollbacks, restore files using reflink copy.ƒ

ƒ These are btrfs only features.


  • Proposal owners:
    • Implement /boot on dedicated ~1G btrfs volume with 'boot' subvolume
    • Design a subvolume layout focusing on snapshot and rollback functionality, and modify the btrfs preset kickstart accordingly.
  • Other developers:
    • Bootloader team to review and ack changes related to /boot.
    • Anaconda to review and merge changes.
    • Might affect dnf snapper plugin behavior.
  • Policies and guidelines: N/A
  • Trademark approval: N/A

Upgrade/compatibility impact

This change will not apply to upgrades.

How To Test

Install and use the system however you usually do, and it should behave the same.

User Experience

  • Transparent in normal use.
  • Always-on integrity verifies metadata and data. Corrupt data results in EIO, it never reaches user space. User is notified by kernel message about affected files by path.
  • Podman can use snapshots (default) or reflinks+overlayfs, at user discretion. Both are faster and more space efficient operations, than copy_up on ext4.
  • Users can opt-in to other btrfs features: snapshots, compression, cp --reflink efficient copies, online scrub, btrfs send/receive, at their own pace.



Contingency Plan

  • Contingency deadline: Revert all changes.
  • Blocks release? Yes.
  • Blocks product? Workstation/KDE are release blocking desktops.


The user is not expected to know btrfs specific things for day to day use.

man 5 btrfs - for information about general btrfs information, mount options, and features.
man btrfs - for information about the btrfs command and sub commands. NOTE: Subcommands can be arbitrarily shortened, as long as it isn't ambiguous. 'btrfs fi us' is the same as 'btrfs filesystem usage'.

Release Notes