Re: [GIT PULL] DRBD for 2.6.32

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

On Sat, Sep 19, 2009 at 3:02 PM, Lars Marowsky-Bree <lmb@suse.de> wrote:
> On 2009-09-19T14:14:30, FUJITA Tomonori <fujita.tomonori@lab.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