[DRBD-user] see replicated data

agag rysic at vp.pl
Thu May 31 14:23:44 CEST 2012

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


I read Guide but not everything is clear for me yet :)

About "understanding how primary-primary" works is not much written:
http://www.drbd.org/users-guide-8.3/s-dual-primary-mode.html.

My first idea is to have in example WWW server and when one crashes, second
is working without any additional admin tasks. But if I don't see the same
data in bouth primary servers (or data is not mounted in secondary) then it
will not work like that... - Yes I can use GFS and centralized database
server and replicate php code files but then DRBD is starting to be not
neaded - am I right?

Second idea is to have almost identical operating systems. For example to
use drbd replicated data for /etc and /bin (wich will be modified only in
primary/first serverd when changes or updates are done). Is it possible
somehow?

Getting a DRBD dual-primary + cluster file systems "right"
is complex, and even if you'd follow a cookbook tutorial on it
still requires understanding of the whole setup, redundancy,
reliable networking and other components,
and reliable and tested fencing and stonith.
What cookbook? Id documentation I see only that good solution for filesystem
is GFS or OCFS2.


Lars Ellenberg wrote:
> 
> On Wed, May 30, 2012 at 07:15:06AM -0700, agag wrote:
>> 
>> I found that I can set two disks as primary and then mount them but if I
>> write anything into mounted drive, then I mus remount disk in second
>> machine.
>> 
>> Any solution?
> 
>  * read the User's Guide
> 
>  * DO NOT use DRBD in dual-primary with cluster file systems,
>    unless you really have to have access to the same data at the same
>    time from both nodes
>  
>  * if you think you need that, reconsider, and go for the simple
>    single-primary failover solution anyways.
> 
> Getting a DRBD dual-primary + cluster file systems "right"
> is complex, and even if you'd follow a cookbook tutorial on it
> still requires understanding of the whole setup, redundancy,
> reliable networking and other components,
> and reliable and tested fencing and stonith.
> 
>> agag wrote:
>> > 
>> > When I connected two drives in two hosts, I have two virtual driver
>> > /dev/drbd1 in every host.
>> > I can mount both but in secondary server it is mounted as read-only (it
>> is
>> > OK in my opinion), but when I write something in drbd1 in primary
>> server,
>> > I can't see anything in secondary. Is it possible to change that
>> begavior?
>> > Can I see in secondary server files to be sure that data is
>> synchronized
>> > and it can be read?
>> > 
>> > I can see that data when I set primary as secondary but is it not so
>> good
>> > idea in my opinion.
>> > 
>> > Without that option I can't also synchronize "Whole system" - in
>> example
>> > /etc (but I'm not sure if it is good idea ;) ).
> 
> -- 
> : Lars Ellenberg
> : LINBIT | Your Way to High Availability
> : DRBD/HA support and consulting http://www.linbit.com
> 
> DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
> __
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> 

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