[Discuss] btrfs

[gaf at blu.org (Jerry Feldman)]

On 02/22/2013 11:01 AM, Rich Pieri wrote:
> 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, assume I have 2 physical volumes, /dev/sda and /dev/sdb.
mkfs.btrfs -d raid1 /dev/sda /dev/sdb
What happens if I get a failure on /dev/sdb.
Assume no snapshots.
>
>> 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).
>


-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
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