A Btrfs field test and workshop

In the Hot Seat

Article from ADMIN 11/2012

By Andreas Kurz

SUSE has officially supported Btrfs in Service Pack 2 of its Enterprise Server 11 since February 2012. Oracle followed soon after with Btrfs support in its own Linux. We explore the possibilities of this young filesystem in detail.

Btrfs is still rated "experimental" in the Linux kernel, and no consumer distributions use it as a preferred filesystem. This is hard to understand, because the designated standard filesystem for Linux offers attractive enterprise-level features that have not been available on Linux from a single source thus far. For a long time, Linux users cast envious glances at ZFS, but with its Sun Common Development and Distribution License, it is not compatible with the GNU General Public License of the Linux kernel.

Preview

I'll start with a brief description of the main features and functions of Btrfs, followed by an installation guide using a virtual instance of Ubuntu 12.04 as an example. Then, I'll demonstrate the main administration tool. Following this, the root filesystem on a test system is converted from ext4 to Btrfs and then converted into a RAID 1. This setup allows a useful demonstration of filesystem snapshots in the course of software updates with a subsequent rollback of the changes.

Enterprise-Level Features

Btrfs is a copy-on-write (COW) filesystem. Whereas a filesystem like ext3 logs block changes in a journal, Btrfs always writes changes to a block at a new location on the disk and references the new data block in the metadata if successful. Only then is the old data released for overwriting, provided it is no longer referenced elsewhere (e.g., by a snapshot).

Btrfs aims not only to offer advanced features but primarily to be fault tolerant, easy to manage, and quickly recoverable if worst comes to worst. It exclusively uses only COW-optimized (B-trees) to manage the metadata and payload, with the exception of the superblock. Btrfs also stores checksums (CRC32C hashes) for data and metadata to detect silent data corruption. Additionally, it provides high-scalability functions targeted at modern

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