Changes/FedoraCloudBtrfsByDefault

Make btrfs the default file system for Fedora Cloud

Summary

For cloud installs of Fedora, we want to provide advanced file system features to users in a transparent fashion. Thus, we are changing the file system for the Cloud Edition to Btrfs so we can leverage its features and capabilities to improve the quality of experience for Cloud users.

Owners

• Name: David Duncan, Chris Murphy, Josef Bacik, Michel Alexandre Salim, Davide Cavalca, Neal Gompa, Dusty Mabe, Matthew Almond
• Email: davdunc@amazon.com, chrismurphy@fedoraproject.org, josef@toxicpanda.com, michel@michel-slm.name, dcavalca@fb.com, ngompa13@gmail.com, dusty@dustymabe.com, malmond@fb.com
• Products: Fedora Cloud Edition
• Responsible WGs: Fedora Cloud WG

Current status

• Targeted release: Fedora Linux 35
• Last updated: 2021-05-24
• 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

Fedora Cloud Edition will switch to using Btrfs for its images. The configuration for the Cloud Edition will match the setup used on the desktop variants, as this has been very well-tested with production deployments across multiple Fedora Linux releases now.

This includes the same subvolume layout that is used on the desktop variants as introduced in Fedora Linux 33, as well as transparent Zstd compression as introduced in Fedora Linux 34.

Benefit to Fedora

The benefits are similar to the ones for Fedora desktop variants; however, there are specific benefits for Fedora Cloud:

• Adds support to Fedora Cloud for the Change to introduce support for Copy-on-Write enhancements to improve performance to package management
• Adds the ability to logically separate contents of the volume without dividing up the available space
  • Transparent compression: significantly reduces write amplification and improves effective I/O throughput
  • Reflinks and snapshots improve efficiency for use cases like containers (CRI-O, containerd, and Podman support both)
• Storage devices can be flaky, resulting in data corruption; Btrfs can help mitigate this
  • Everything is checksummed and verified on every read
  • Corrupt data results in EIO (input/output error), instead of resulting in application confusion, and isn’t replicated into backups and archives
• Improves system responsiveness under pressure
  • Btrfs has been tested in production to have proper IO isolation capability via cgroups2
  • Completes the resource control picture: memory, cpu, IO isolation
• File system resize
  • Online shrink and grow are cornerstones of the Btrfs design
• Complex storage setups are… complicated
  • Simple and comprehensive command interface. One master command
  • Simpler to boot, all code is in the kernel, no initramfs complexities
  • Simple and efficient file system replication, including incremental backups, with btrfs send and btrfs receive

Scope

• Proposal owners:
  • Submit PRs for Cloud Edition kickstarts to produce disk images using Btrfs.
• Release engineering: #NNNN
• Policies and guidelines: N/A
• Trademark approval: N/A

Upgrade/compatibility impact

Change will not affect upgrades.

How To Test

Once the change lands in Rawhide, spin up the images in AWS, GCP, and KVM/OpenStack to test to see systems boot and run.

User Experience

• Mostly transparent.
• Space savings and extend hardware life, via compression.
• Utilities for used and free space are expected to behave the same. No special commands are required.
• More detailed information can be revealed by btrfs specific commands.
• cp command will create reflink copies by default.

Dependencies

None.

Contingency Plan

• Contingency mechanism: Owner will revert changes back to the previous ext4 configuration
• Contingency deadline: Beta freeze
• Blocks release? Yes
• Blocks product? Cloud

Documentation

Strictly speaking, no extra documentation is required reading for users.

Release Notes

The default file system on the cloud is now Btrfs, following the desktop change in Fedora Linux 33. Fedora Server, IoT, and CoreOS are still specifically excluded.