Re: [PATCH 1/4] md: Factor out RAID6 algorithms into lib/

[Dan Williams <dan.j.williams@intel.com>]

On Sat, Jul 18, 2009 at 11:42 AM, David Woodhouse<dwmw2@infradead.org> wrote:
> On Sat, 18 Jul 2009, Dan Williams wrote:
>> I was under the impression that btrfs wanted to leverage md's stripe
>> handling logic as well, seems that is not the case?
>
> No. We do a bunch of the stuff you mention above, but entirely within the
> file system so we don't have to invent a bunch of layering violations just
> to work around a broken design.

Sure, a layering violation for an existing filesystem.  For btrfs, at
LSF'09, we briefly talked about breaking out more than just the
erasure codes from software-raid into a "libraid".  At some point in
the i/o path a btrfs stripe operation becomes indistinguishable from a
raid5,6 operation so at first glance there appears to be room to share
common infrastructure like portions of handle_stripe for example.

--
Dan