[DRBD-user] Creating a "degraded" DRBD (was: Staggered implementation questions.)

Lars Ellenberg lars.ellenberg at linbit.com
Thu Dec 4 15:29:05 CET 2008

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


On Thu, Dec 04, 2008 at 11:12:30AM +0100, Stefan Seifert wrote:
> On Thursday, 04. December 2008, Peter Funk wrote:
> > Hello,
> >
> > Corey Brown asked on Friday, 28.11.2008 13:50:
> > > Can you load a Linux  server with drbd as the primary server then add on
> > > the secondary server later ?
> 
> Yes, it just works. A few details should be heeded though.
> 
> > Yesterday I have for the first time tried to achieve creating a
> > degraded DRBD and hopefully I think, I succeded:
> > This is on a freshly installed Ubuntu 8.04.1 LTS which came with
> > a 8.0.11 DRBD package.
> 
> Please, always use the latest version. That's 8.0.14 for the 8.0 branch. You 
> might even consider upgrading to 8.2.7. The verify feature should be worth 
> it.

though it may blow up [again :(] if it finds something out of sync,
unless you also patch it with
http://git.drbd.org/?p=drbd-8.2.git;a=commitdiff;h=1174410d144a88e920b81ca0a16562fc9b89479c

> If you really want to do high availability, you should go all the way. I'm 
> speaking from experience. You don't want to hit one of drbd's known bugs when 
> you least need it. That is, when something happens and a node goes down.
> 
> > Of course I had to prepare the /etc/drbd.conf first.
> > To create the DRBD device (resource) on this single side server
> > (assuming the DRBD network is disconnected) I used the
> > following commands:
> >     drbdadm create-md r0
> >     drbdadm down r0
> >     cat /proc/drbd
> >     drbdadm -- ::::1:1:::: set-gi r0
> >     drbdadm up r0
> >     drbdadm primary r0
> >     cat /proc/drbd
> 
> If you leave out the diagnostic commands, you'll see that you end up with just 
> about the same commands as in the excellent drbd user's guide. The point is: 
> drbd just doesn't need a secondary. So if you leave it out, it'll just do 
> with one node.
> 
> Of course, the second node should already be in drbd.conf (don't know, if it 
> would work without).

you can place a "dummy" there,
until you know final hostname and ip addresses.
but the section needs to be there.

> If you plan on running with one node only for some time, 
> you'll also want to set the wfc-timeout and degr-wfc-timeout to small but 
> positive values, so drbd wouldn't wait long for the second node to appear 
> when starting up.

glad to see so many people giving good answers on this list.

cheers,

-- 
: 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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