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F.A.Q.
p. 260
large ones, extremely slow, and also there’s no internal protection mechanism as one disk is seen as
a single entity by the filesystem itself.
BTRfs instead uses “chunks”. Each disk, regardless its size, is divided into pieces (the chunks) that are
either 1 GiB in size (for data) or 256 MiB (for metadata). Chunks are then grouped in block groups,
each stored on a different device. The number of chunks used in a block group will depend on its
RAID level. And here comes another awesome feature of BTRfs: the volume manager is directly
integrated into the filesystem, so it doesn’t need anything like hardware or software raid, or volume
managers like LVM. Data protection and striping is done directly by the filesystem, so you can have
different volumes that have inner redundancy:
BTRfs allocation tree
For example, Block group 2 is configured for RAID1 redundancy. So, a chunk is consumed on disk1,
and its mirror is stored in another device, Disk 2 in the picture. In this way, if we lose Disk1, another
copy of the block is still available on Disk2, and another copy can be immediately recreated for
example on Disk3 using the free chunk. You can configure BTRfs for File Striping, File Mirroring, File
SMirroring, Striping with Single and Dual Parity.
Another aspect of BTRfs is its performance. Because of its modern design and the b-tree structure,
BTRfs is damn fast. If you didn’t already, look at the video above starting from 30:30. They have run
a test against the same storage, formatted at different stages with XFS, EXT4 and BTRfs, and they