[DRBD-user] allow-two-primary on ext3

[Pavlos Parissis]

Hi,

I am having 3 nodes and 2 resources and I want to have the third node as the
secondary for both resources.
Here is the /etc/drbd.conf, which is common on all nodes
#
# please have a a look at the example configuration file in
# /usr/share/doc/drbd83/drbd.conf
#

global {
  usage-count yes;
}
common {
  protocol C;
}
resource drbd_pbx_service_1 {
  on node-01 {
    device    /dev/drbd1;
    disk      /dev/sdb1;
    address   10.10.10.129:7789;
    meta-disk internal;
  }
  on node-03 {
    device    /dev/drbd1;
    disk      /dev/sdb1;
    address   10.10.10.131:7789;
    meta-disk internal;
  }
}

resource drbd_pbx_service_2 {
  on node-02 {
    device    /dev/drbd2;
    disk      /dev/sdb1;
    address   10.10.10.130:7790;
    meta-disk internal;
  }
  on node-03 {
    device    /dev/drbd2;
    disk      /dev/sdc1;
    address   10.10.10.131:7790;
    meta-disk internal;
  }
}

My initial situation was as follows, node-01 primary for drbd_pbx_service_1
resource and node-02 primary for drbd_pbx_service_2 resource.
I tried to get the node-03 as primary for both resources but I got the error
message " Multiple primaries not allowed by config"
here is the steps which I followed

[root at node-01 ~]# drbd-overview
  1:drbd_pbx_service_1  Connected Primary/Secondary UpToDate/UpToDate C
r----


[root at node-03 etc]# drbd-overview
  1:drbd_pbx_service_1  Connected Secondary/Secondary UpToDate/UpToDate C
r----
  2:drbd_pbx_service_2  Connected Secondary/Primary   UpToDate/UpToDate C
r----

[root at node-03 etc]# drbdadm primary drbd_pbx_service_1

[root at node-03 etc]# drbd-overview
  1:drbd_pbx_service_1  Connected Primary/Secondary UpToDate/UpToDate C
r----
  2:drbd_pbx_service_2  Connected Secondary/Primary UpToDate/UpToDate C
r----

[root at node-03 etc]# drbdadm primary drbd_pbx_service_2
2: State change failed: (-1) Multiple primaries not allowed by config
Command 'drbdsetup 2 primary' terminated with exit code 11

I read the manual for allow-two-primary settings and basically states that I
can't do what I want, since I use ext3 fs on drbd devices.
But, I don't quite understand why, since these 2 resources are running on
different disks and over different connections. I don't understand how the
FS on them will get corrupted.

I am in the process of evaluation a 3 node cluster (Redhat or
heartbeat/pacemaker not decide yet) which will have 2 resources and these 2
resources will use different active nodes but the same standby node. So, I
want to see if I can use DRBD as my storage solution since I can't utilize a
shared storage.

Thanks,
Pavlos Parissis
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