13.4.1. Support for the btrfs File System
Btrfs is a copy-on-write (CoW) general purpose file system. Based on the CoW functionality, btrfs provides snapshoting. Beyond that data and metadata checksums improve the reliability of the file system. btrfs is highly scalable, but also supports online shrinking to adopt to real-life environments. On appropriate storage devices btrfs also supports the TRIM command.
Support
With SUSE Linux Enterprise 11 SP2 the btrfs file system is supported as root file system, i.e. the file system for the operating system, across all architectures of SUSE Linux Enterprise 11 SP2. Customers are advised to use the YaST partitioner (or AutoYaST) to build their systems: YaST will prepare the btrfs file system for use with subvolumes and snapshots. Snapshots will be automatically enabled for the root file system using SUSE's snapper infrastructure. For more information about snapper, it's integration into ZYpp and YaST, and the YaST snapper module, see the SUSE Linux Enterprise documentation.
Offline-Migration from existing "ext" file systems (ext2, ext3, ext4) is supported.
RAID
Btrfs is supported on top of MD (multiple devices) and DM (device mapper) configurations. Please use the YaST partitioner to achieve a proper setup.
Future Plans
- We are planning to announce support for btrfs' built-in multi volume handling and RAID in a later version of SUSE Linux Enterprise.
- Transparent compression is implemented and mature. We are planning to support this functionality in the YaST partitioner in a future release.
- We are commited to actively work on the btrfs file system with the community, and we keep customers and partners informed about progress and experience in terms of scalability and performance. This may also apply to cloud and cloud storage infrastructures.
Online Check and Repair Functionality
Check and repair functionality ("scrub") is available as part of the btrfs command line tools. "Scrub" is aimed to verify data and metadata assuming the tree structures are fine. "Scrub" can (and should) be run periodically on a mounted file system: it runs as a background process during normal operation.
With the release of SUSE Linux Enterprise 11 SP2, the long awaited "fsck.btrfs" tool is available in the SUSE Linux Enterprise update repositories.
Capacity Planning
If you are planning to use btrfs with its snapshot capability, it is advisable to reserve twice as much disk space than the standard storage proposal. This is automatically done by the YaST2 partitioner for the root file system.
Hard Link Limitation
In order to provide a more robust file system, btrfs incorporates back references for all file names, eliminating the classic "lost+found" directory added during recovery. A temporary limitation of this approach affects the number of hard links in a single directory that link to the same file. The limitation is dynamic based on the length of the file names used. A realistic average is approximately 150 hard links. When using 255 character file names, the limit is 14 links. We intend to raise the limitation to a more usable limit of 65535 links in a future maintenance update.
More information about btrfs can be found in the SUSE Linux Enterprise 11 documentation.
