< Changes
Enable btrfs transparent zstd compression by default
Summary
On variants using btrfs as the default filesystem, enable transparent compression using zstd. Compression saves space and can significantly increase the lifespan of flash-based media by reducing write amplification. It can also increase read and write performance.
Owners
- Name: Michel Salim, Davide Cavalca, Josef Bacik
- Email: michel@michel-slm.name, dcavalca@fb.com, josef@toxicpanda.com
Current status
- Targeted release: Fedora 34
- Last updated: 2021-01-06
- FESCo issue: <will be assigned by Wrangler>
- Tracker bug: <will be assigned by Wrangler>
- Release notes tracker: <will be assed by Wrangler>
Detailed description
Transparent compression is a btrfs feature that allows a btrfs filesystem to apply compression on a per-file basis. Of the three supported algorithms, zstd is the one with the best compression speed and ratio. Enabling compression saves space, but it also reduces write amplification, which is important for SSDs. Depending on the workload and the hardware, compression can also result in an increase in read and write performance.
See https://pagure.io/fedora-btrfs/project/issue/5 for details. This was originally scoped as an optimization for https://fedoraproject.org/wiki/Changes/BtrfsByDefault during Fedora 33.
Feedback
Why use zstd:1 specifically?
https://hackmd.io/kIMJv7yHSiKoAq1MPcCMdw has an analysis of the various compression levels and their impact, both in terms of CPU usage and disk space savings.
Benefit to Fedora
Better disk space usage, reduction of write amplification, which in turn helps increase lifespan and performance on SSDs and other flash-based media. It can also increase read and write performance.
Scope
- Proposal owners:
- Update anaconda to perform the installation using
mount -o compress=zstd:1 - Set the proper option in fstab (alternatively: set the XATTR)
- Update disk image build tools to enable compression:
- lorax
- appliance-tools
- osbuild
- imagefactory
- [optional] Add support for setting compression level when defragmenting
- [optional] Add support for setting compression level using
btrfs property
- Update anaconda to perform the installation using
- Other developers:
- anaconda: review PRs as needed
- Release engineering: https://pagure.io/releng/issue/9920
- Policies and guidelines: N/A
- Trademark approval: N/A
Upgrade/compatibility impact
This Change only applies to newly installed systems. See How to test for converting an existing system.
How to test
Existing systems can be converted to use compression manually with btrfs filesystem defrag -czstd -r, updating /etc/fstab to add the compress=zstd:1 mount option and remounting (mount -o remount /)
User experience
Compression will result in file sizes (e.g. as reported by du) not matching the actual space occupied on disk. The compsize utility can be used to examine the compression type, effective compression ration and actual size.
Dependencies
Anaconda will need to be updated to perform the installation using mount -o compress=zstd:1
Contingency plan
- Contingency mechanism: will not include PR patches if not merged upstream and will not enable
- Contingency deadline: Final freeze
- Blocks release? No
- Blocks product? No
Documentation
https://btrfs.wiki.kernel.org/index.php/Compression
Release Notes
Transparent compression of the filesystem using zstd is now enabled by default. Use the compsize utility to find out the actual size on disk of a given file.