[Discuss] btrfs

[warlord at MIT.EDU (Derek Atkins)]

Rich,

Rich Pieri <richard.pieri at gmail.com> writes:

> On Mon, 25 Feb 2013 10:53:28 -0500
> Derek Atkins <warlord at MIT.EDU> wrote:
>
>> How is it still raid1?
>
> What Btrfs calls "RAID" isn't actually RAID. It isn't redundant disks.
> What Btrfs calls "RAID" is actually striped or mirrored data and
> metadata. 
>
> Say that you have four devices in a Btrfs volume. There are three
> different ways that you can configure data storage for the volume. Pay
> attention because this is quite different from what ZFS does.
>
> The first is what Btrfs calls data raid0: striped data. In this
> configuration, if you write a large file then the file extents will be
> distributed across all four devices in the volume as evenly as possible.
>
> The second is what Btrfs calls raid1: mirrored data. In this
> configuration, a given file is assigned to two devices in the volume,
> with all data written to both devices. It should be noted that devices
> are not mirrored. In a three device raid1 volume, file1 may be written
> to sda and sdb while file2 may be written to sda and sdc, and file3 may
> be on sdb and sdc. The three device raid1 is a great way to demonstrate
> the nature of Btrfs data and metadata mirroring as different from
> traditional and ZFS RAID1.
>
> The third is what Btrfs calls raid10: striped and mirrored data. In this
> configuration, a large file's extents will be distributed across all
> four devices in the volume, just like raid0. In addition, a replica of
> each extent will be written to a different device. Both copies of the
> file are striped across the entire volume. Reads are balanced across
> all devices in the volume.
>
> Btrfs raid10 requires at least four devices but can have more
> than that including odd numbers of devices.

Thank you for the detailed description.  Could you give (or point me to)
a brief description of how ZFS's RAID differs from these configurations?

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
       warlord at MIT.EDU                        PGP key available