[DRBD-user] Split brain auto recovery with DRBD9

Mark Wu wudx05 at gmail.com
Wed Mar 2 07:11:11 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.

Thanks Digimer!

I will learn more about DRBD's fencing mechanism.

On Wed, Mar 2, 2016 at 12:10 PM, Digimer <lists at alteeve.ca> wrote:

> On 01/03/16 08:56 PM, Mark Wu wrote:
> > Hi Digimer,
> >
> > Thanks for your reply!
> >
> > Yes,  I understand fencing can prevent split-brains.  But in my case it
> > maybe not sufficient.  Let me clarify my use case.  Basically, you can
> > get the architecture from http://ibin.co/2YoKo5VOmRYn    The app on each
> > client server will do I/O via block interface directly instead using a
> > cluster file system. Every client server need write access to all drdb
> > volumes to build a VG group. But the application can guarantee that no
> > two servers write to the same data area at the same time because it just
> > writes to the data belonging to itself even when spli-brain happens.  So
> > merging data I mentioned before means just pull all newest data from
> > different volumes together.
> >
> > For the suggestion of fencing,  I think it still can cause somehow
> > out-of-sync because the fencing is invoked by cluster management
> > software, but in data plane the I/O could be done before the fencing
> > happens.
> >
> > my understanding is that fencing is invoked by the cluster management
> > software asynchronously.
> First; My experience is with 8.4, not 9. So caveat emptor.
> DRBD has its own concept of fencing; 'fencing; resource-and-stonith;'
> and 'fence-handler "/path/to/some/script";'. If DRBD detects the peer
> fail, it blocks IO and calls the fence handler immediately. Most often,
> this handler passes the request up to the cluster manager and waits for
> a success message.
> So no, DRBD will not fall out of sync.
> As for your use case; I honestly don't understand it. It looks rather
> complicated.
> --
> Digimer
> Papers and Projects: https://alteeve.ca/w/
> What if the cure for cancer is trapped in the mind of a person without
> access to education?
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