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Message-ID: <e9c3a7c20909191656p625ccfa4pcef94cbe8a232bae@mail.gmail.com>
Date: Sat, 19 Sep 2009 16:56:15 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Lars Marowsky-Bree <lmb@...e.de>
Cc: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
jens.axboe@...cle.com, neilb@...e.de, hch@...radead.org,
James.Bottomley@...e.de, lars.ellenberg@...bit.com,
linux-kernel@...r.kernel.org, drbd-dev@...ts.linbit.com,
akpm@...ux-foundation.org, bart.vanassche@...il.com,
davej@...hat.com, gregkh@...e.de, kosaki.motohiro@...fujitsu.com,
kyle@...fetthome.net, torvalds@...ux-foundation.org,
nab@...ux-iscsi.org, knikanth@...e.de, philipp.reisner@...bit.com,
sam@...nborg.org
Subject: Re: [GIT PULL] DRBD for 2.6.32
On Sat, Sep 19, 2009 at 3:02 PM, Lars Marowsky-Bree <lmb@...e.de> wrote:
> On 2009-09-19T14:14:30, FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:
>
>> I guess that Christoph is worry about adding another user interface
>> for kinda device management; once we merge this, we can't fix it (for
>> the raid unification).
>
> Why can't it be fixed?
>
> Either
>
> a) there's going to be a transition period during which the "old"
> interface is supported but depreciated and scheduled to be removed (all
> driving the new unified same back-end),
>
> or b) there's going to be a new kernel which requires new user-space
> tools sharp.
>
> In either case, dm/md are affected by this, so a third interface doesn't
> really make much difference. The refactoring needs to happen in the
> back-end anyway, and that actually becomes easier when all concurrent
> implementations are present and can be reworked at the same time.
It's actually four "raid" implementations in the kernel if you count
the multiple-disk functionality of btrfs. The precedent is already
set for merging new multiple-disk management interfaces.
Neil has come the closest to actually trying to start (i.e. code) the
unification effort [1] and that was for the relatively straightforward
case of mapping the dm-raid5 backend to md-raid5... no uptake to date.
There are no strictly equivalent drbd-backends in the kernel
presently, so leaving this out of tree is a net-loss for mainline.
--
Dan
[1]: http://marc.info/?l=dm-devel&m=124567352518676&w=2
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