1
2	BTRFS
3	=====
4
5Btrfs is a new copy on write filesystem for Linux aimed at
6implementing advanced features while focusing on fault tolerance,
7repair and easy administration. Initially developed by Oracle, Btrfs
8is licensed under the GPL and open for contribution from anyone.
9
10Linux has a wealth of filesystems to choose from, but we are facing a
11number of challenges with scaling to the large storage subsystems that
12are becoming common in today's data centers. Filesystems need to scale
13in their ability to address and manage large storage, and also in
14their ability to detect, repair and tolerate errors in the data stored
15on disk.  Btrfs is under heavy development, and is not suitable for
16any uses other than benchmarking and review. The Btrfs disk format is
17not yet finalized.
18
19The main Btrfs features include:
20
21    * Extent based file storage (2^64 max file size)
22    * Space efficient packing of small files
23    * Space efficient indexed directories
24    * Dynamic inode allocation
25    * Writable snapshots
26    * Subvolumes (separate internal filesystem roots)
27    * Object level mirroring and striping
28    * Checksums on data and metadata (multiple algorithms available)
29    * Compression
30    * Integrated multiple device support, with several raid algorithms
31    * Online filesystem check (not yet implemented)
32    * Very fast offline filesystem check
33    * Efficient incremental backup and FS mirroring (not yet implemented)
34    * Online filesystem defragmentation
35
36
37
38	MAILING LIST
39	============
40
41There is a Btrfs mailing list hosted on vger.kernel.org. You can
42find details on how to subscribe here:
43
44http://vger.kernel.org/vger-lists.html#linux-btrfs
45
46Mailing list archives are available from gmane:
47
48http://dir.gmane.org/gmane.comp.file-systems.btrfs
49
50
51
52	IRC
53	===
54
55Discussion of Btrfs also occurs on the #btrfs channel of the Freenode
56IRC network.
57
58
59
60	UTILITIES
61	=========
62
63Userspace tools for creating and manipulating Btrfs file systems are
64available from the git repository at the following location:
65
66 http://git.kernel.org/?p=linux/kernel/git/mason/btrfs-progs.git
67 git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-progs.git
68
69These include the following tools:
70
71mkfs.btrfs: create a filesystem
72
73btrfsctl: control program to create snapshots and subvolumes:
74
75	mount /dev/sda2 /mnt
76	btrfsctl -s new_subvol_name /mnt
77	btrfsctl -s snapshot_of_default /mnt/default
78	btrfsctl -s snapshot_of_new_subvol /mnt/new_subvol_name
79	btrfsctl -s snapshot_of_a_snapshot /mnt/snapshot_of_new_subvol
80	ls /mnt
81	default snapshot_of_a_snapshot snapshot_of_new_subvol
82	new_subvol_name snapshot_of_default
83
84	Snapshots and subvolumes cannot be deleted right now, but you can
85	rm -rf all the files and directories inside them.
86
87btrfsck: do a limited check of the FS extent trees.
88
89btrfs-debug-tree: print all of the FS metadata in text form.  Example:
90
91	btrfs-debug-tree /dev/sda2 >& big_output_file
92