[Xen-devel] [BUG] Xen Remus, DRBD Protocol D and old Linux kernels

[Pato SÃinz <superpato.sainz@xxxxxxxxx>]

Good evening, people.

More than a bug, it's an issue, a big one IMO.

Even though information on the Remus project and its implementation is kind of
scarce on the internet and is usually outdated (the project could use some love
on that side of things, though it seems that on the coding side, it's
still being
properly maintained), there's a huge problem in the current implementation: its
storage depends on a custom patch developed for a very old version of DRBD.

Currently, the wiki points that in order to use Remus you must use it
with a custom
version of DRBD, forked from 8.3.11 (and there's also a patch for
8.3.9). Support
for these versions have been dropped for almost 3 years, and they are only
compatible with Linux kernels 3.0-3.4: most distros have already dropped these
kernels and deleted them from their repositories: even kernel.org plans to drop
support for the 3.4 kernel in September this year. Building your own is an
unnecessary hassle.

These problems make Remus practically unusable, despite being one of the
coolest features Xen has in my honest opinion.

This issue has also been brought up at least once on the DRBD mailing list[1]
and until there's more cooperation between the Xen project and LINBIT to
develop a more robust Protocol D, they've refused to pull the patch into their
tree to be maintained.

It's worth noting that the "official" patch (by rshiriam) is somewhat
simple[2][3].

A solution to this for the short term would be to port the patch to the current
DRBD version (8.4.7-1) and in the long term, to collaborate with LINBIT so
the Xen project doesn't have to maintain their own downstream changes, and
we benefit from LINBIT's experience on realiable storage.

The short term solution seems like a very quick one, since the original patch
is small-ish, and I've been trying to do it[4] but simply C isn't my strong suit
and I don't know much of DRBD's source, even after doing a cursory reading
of it.

I know this is an open source project and thus most developers are
volunteers, but
this kind of issue really is a show-stopper that keeps me (and presumably many
other people) from using the awesome feature that Remus is.

[1]: http://lists.linbit.com/pipermail/drbd-user/2013-October/020370.html
[2]: 
http://remusha.wdfiles.com/local--files/configuring-and-installing-remus/drbd-8.3.9-remus.patch
[3]: 
https://github.com/macrosheep/remus-drbd/commit/2685b294f5b416d827bdf446a69c88ab04df50dd
[4]: https://github.com/superpatosainz/remus-drbd

-- 
Pato SÃinz - @superpatosainz

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