Rich, Rich Pieri <richard.pi...@gmail.com> writes:
> On Mon, 25 Feb 2013 10:53:28 -0500 > Derek Atkins <warl...@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 warl...@mit.edu PGP key available _______________________________________________ Discuss mailing list Discuss@blu.org http://lists.blu.org/mailman/listinfo/discuss