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

Stefan Seifert nine at detonation.org
Thu Dec 4 11:12:30 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 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.

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). 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.

Regards,
Stefan



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