[DRBD-user] Regarding an old 2013 thread about Protocol D

Pato Sáinz superpato.sainz at gmail.com
Sun Jan 17 06:09:06 CET 2016

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

Good evening,

I've recently started a thread[1] at the Xen-devel list regarding DRBD
and the Protocol D, necessary for Remus, the High Availability/clustering
feature of Xen. The thread outlines in a nutshell the following problems
relevant to DRBD:

I. Remus depends on a patched version of DRBD[2]. That patch is only
available for DRBD 8.3.9 and 8.3.11.

II. This means that in order to use Remus, you must use versions
3.0 through 3.4 of the Linux kernel. Currently there's no distro that
support these versions and even kernel.org sets its end of support
for 3.4 in September of the present year.

Now, researching this "Protocol D" I've found an old thread[3] in this very
list, requesting the implementation of this feature into the tree:

Lars pointed out that there may be some issues with that patch and he
explained how he didn't think it was a priority in the near-term back then.

He encouraged readers to "try and convince him" that Proto D should be
implemented, but nobody replied.

It's a shame that Remus is stuck in such old kernels (even though it's
still a pretty well maintained feature in the Xen tree) and that still, if
someone was to use it and downgrade significantly their kernel,
you'd have to use a version of DRBD that even LINBIT has dropped
paid support for it.

I think Protocol D should be implemented because:

I. Remus is actually "the coolest thing that happened to the combination
of virtualization + HA, ever". And there aren't many other alternatives
for this (Remus is supported by Xen in their main tree, too).

II. The original Protocol D patch was relatively small and shouldn't take
too many man-hours to implement (and I can offer my help to test its
reimplementation, so did Eugene Istomin back in 2013).

III. In case any developers don't feel sure about Protocol D's consistency,
it still could be enabled via a special Makefile target, #ifdef, or maybe
implemented in a branch outside git master. It would even make a nice
9.0 feature.

Anyway, I want to thank everybody at LINBIT for making such a nice
piece of software, I use it on production and it works really well.

[1]: http://lists.xenproject.org/archives/html/xen-devel/2016-01/msg01820.html
[2]: https://github.com/rshriram/remus-drbd
[3]: http://lists.linbit.com/pipermail/drbd-user/2013-October/020370.html

Pato Sáinz - @superpatosainz

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