[DRBD-user] 3 node stacked setup and dual primary issues

Lars Ellenberg lars.ellenberg at linbit.com
Mon Mar 18 10:19:08 CET 2013

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

On Fri, Mar 15, 2013 at 10:22:19AM +0100, Cristian Mammoli wrote:
> Hi, as far as I understand a 3 node steup with dual primary and 3rd
> node for disaster recovery is not possible:
> http://www.gossamer-threads.com/lists/drbd/users/22188#22188
> So I tried the following setup as suggested by Lars:

(actually, I suggested to reconsider the "need" for dual Primary...)

> drbd-1: (first node)
> drbd-2: (second node)
> drbd-dr: (disaster recovery node)
> drbd-1 and drbd-2 should be Primary/Primary (I need it as a backing
> store for kvm VMs)
> drbd-2 replicates with drbd-dr in Primary/Secondary mode and protocol A
> drbd-2 replicates resource stacked on the previous one with drbd-1
> and protocol C
> Scheme:
> drbd1 <---C--->	drbd1
> 		drbd0 ---A---->	drbd0	
> node-drbd-1	node-drbd-2	node-drbd-dr
> The resources start up and sync. The i tried the following:
> format drbd1 device on drbd-1
> mount drbd1 device on drbd-1
> create test file drbd-1-test
> umount drbd1 device on drbd-1
> mount drbd1 device on drbd-2
> create test file drbd-2-test
> I can see both drbd-1-test and drbd-2-test
> umount drbd1 device on drbd-2
> demote and stop stacked drbd1 resource on drbd-1 and drbd-2
> promote drbd0 resource on drbd-dr
> mount drbd0 device on drbd-dr
> create test file drbd-dr-test
> I can see drbd-1-test drbd-2-test drbd-dr-test
> demote drbd0 resource on drbd-dr
> start and promote drbd1 resource on drbd-1 and drbd-2
> mount drbd1 on drbd-2
> I can see drbd-1-test drbd-2-test drbd-dr-test
> umount drbd1 on drbd-2
> mount drbd1 on drbd-1
> I can see drbd-1-test drbd-2-test ONLY!!
> If I invalidate the resource on drbd-1 and do a full resync the 3rd
> file appear.

Design limitation in DRBD 8.x and this setup.

For recovery, you need to do extra steps
(and if you know how, you can avoid some full sync).
You'd better consult with us first, before trying to pull this off.

With DRBD 9, we plan to have this deployment covered without the hacks,
but it will be some time yet, until 9 is good for production.

: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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