[Discuss] btrfs

[richard.pieri at gmail.com (Rich Pieri)]

On Fri, 22 Feb 2013 10:04:24 -0500
Jerry Feldman <gaf at blu.org> wrote:

> Most of the examples I have seen are to install btrfs on raw drives.

Btrfs is, like ZFS, both file system and volume manager. There is
typically no benefit to not allowing Btrfs to manage entire devices
unless you need to have part of the disk not be Btrfs. Not allowing
Btrfs to manage whole devices makes it more difficult to replace
faulted devices.

> redundant,, but your data is essentially stripped (RAID0) so you
> effectively get more storage with the safety of RAID1. (You can
> configure btrfs to be fully redundant if you want to).

No. RAID0 means a device failure equals data loss. Mirrored metadata
will not save you from that. What mirrored metadata gets you is a
measure of protection against bit errors damaging file names,
permissions, checksums and related information.

Note that Btrfs mirrors data and metadata, not disks or disk blocks. A
three-disk Btrfs raid1 is not three copies of every file extent. It is
two copies of every file extent stored one each on two out of the three
disks.

> So, our typical install at an installfest is to a single drive,
> possibly with a pre-existing Windows on a laptop. What might be the
> advantage of using btrfs today over ext4 for a new user. Fedora 18
> certainly gives you the option of using ext4 or btrfs.

https://btrfs.wiki.kernel.org/index.php/Main_Page

> A more detailed question is using btrfs on an install in a single or
> multi-disk clean install from scratch, can you set up a btrfs as boot
> drive. AFAIK, yes, but I have seen issues online. One issue is that
> btrfs automatically compresses files, but GRUB needs stuff not to be
> compressed.

Compression is currently an all or nothing deal across an entire Btrfs
volume (modulo some chattr tricks). Subvolume compression is in the
works. This will allow for uncompressed /boot subvolume and
compressed /home subvolume (for example).

-- 
Rich P.