[DRBD-user] Help with recovering from network failure (failover and back again)

Guus Houtzager guus at houtzager.net
Tue Sep 13 22:21:48 CEST 2005

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


Hi,

On Tue, 2005-09-13 at 11:06 +0200, Philipp Reisner wrote:
> Hi, 
> 
>   In the moment when you disconnect the device pair and fs1 is primary
>   we have to assume that the data is modified on fs1.
>   It is not possible to do a gracefull switchover while fs1 and fs2 
>   are disconnected. 
> 
>   What you do with the "gracefull switchover" seems to the algorithms
>   of DRBD-0.7 as split brain situation. In DRBD-0.7 there is a 
>   auto-recover logic implemented, that says: the node that was
>   primary at split brain time, has the good data.

Ah, that explains things!

>   To really understand what goes on, please read the
>  http://www.drbd.org/fileadmin/drbd/publications/drbd_paper_for_NLUUG_2001.pdf
>   paper. And... there are tools to modify the GCs __offline__ (this means
>   /etc/init.d/drbd stop!! )

I'll read that.

>   All this got fixed in drbd-8. There you would express, what you want
>   with these config statements:
> 
>   after-sb-0pri discard-older-primary;
>   after-sb-1pri consensus;
>   after-sb-2pri disconnect;
> 
>   [ See item 5 of http://svn.drbd.org/drbd/trunk/ROADMAP ]
> 
> The bottom line: This is a shortcomming of drbd-0.7, that is already
> fixed in drbd-8 . DRBD-8 is not yet ready....

Ok, that's good to know. For now I'll tinker a bit with manual
invalidating one side. That will cost me a full resync when
reconnecting, but as long as it works as I want, that's no big problem
for now. I'm not expecting very frequent netwerk trouble. I'm at the
designing / testing fase of the project, so knowing that it will work
with 0.8 is good enough, I'll try to work around it for now.

I glanced over the roadmap and saw a lot of items with percentages
complete :) Do you have a date in mind for the release of 0.8? A few
months from now or something like early 2006?

> -Philipp

Thanks for your time and effort!

Regards,

-- 
Guus Houtzager                           Email: guus at houtzager.net
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        --Rincewind, The Light Fantastic




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