[DRBD-user] Dual primary question.

[Richard Whittaker]

Hi all:

I am new to DRBD, and I think I have it setup correctly, but wanted to 
check my assumptions at the door. I have two nodes connected over a VPN 
link, and they are geographically separated by about 15 kilometres. 
Their connection is not mind blowingly fast, but I am not looking for 
true realtime I/O. I am looking to replicate, at the block level, a 
qmail messaging store between the two nodes, and I like the idea of 
block level replication, because if a message comes in, I don't have to 
replicate the user's entire message store like I believe Unison would do.

Block level replication would also be, I believe truly bi-directional.

So, for my testing I have created a dual primary drbd called /dev/drbd1.

Looking at /proc/drbd on both nodes shows an active Primary/Primary device.

[root at defiant tmp]# cat /proc/drbd
version: 8.3.15 (api:88/proto:86-97)
GIT-hash: 0ce4d235fc02b5c53c1c52c53433d11a694eab8c build by 
mockbuild at builder17.centos.org, 2013-03-27 16:04:08

  1: cs:Connected ro:Primary/Primary ds:UpToDate/UpToDate C r-----
     ns:1728 nr:524052 dw:525780 dr:5798 al:4 bm:44 lo:0 pe:0 ua:0 ap:0 
ep:1 wo:b oos:0
[root at defiant tmp]#

  The device is mounted on both systems.

/dev/drbd1 on /var/tmp type ext3 (rw)

The config on both nodes is identical.

global {
         usage-count yes;
         }

common {
         protocol C;
}

resource mailstore {

         net {
                 allow-two-primaries;
                 after-sb-0pri discard-least-changes;
                 after-sb-1pri discard-secondary;
                 }
         startup {
                 become-primary-on both;
                 }

         on defiant.avits.ca {
         device  /dev/drbd1;
         disk /dev/sdc;
         address 192.168.0.4:7789;
         meta-disk internal;
         }
         on illustrious.avits.ca {
         device /dev/drbd1;
         disk /dev/sdb;
         address 192.168.64.4:7789;
         meta-disk internal;
         }
}

Now to my logic, if I write a file to one node, it should show up on the 
other. So on 192.168.0.4, I do an ls -l /etc >/var/tmp/blah.txt, it 
should show up on BOTH systems with the same size and date stamp.

...Node 1.

[root at defiant tmp]# ls -l /etc >/var/tmp/blah.txt
[root at defiant tmp]# ls -l /var/tmp
total 16
-rw-r--r-- 1 root root 15893 Apr 17 10:53 blah.txt
[root at defiant tmp]#

...Node 2.
[root at illustrious ~]# ls -l /var/tmp
total 32
drwx------ 10 vpopmail vchkpw  4096 Nov 17 21:09 avits.ca
-rw-r--r--  1 vpopmail vchkpw   165 Apr 16 13:46 blah3.txt
-rw-r--r--  1 vpopmail vchkpw  2532 Apr 16 13:55 blah.txt
drwx------  5 vpopmail vchkpw  4096 Aug 14  2013 example.com
drwx------ 21 vpopmail vchkpw 16384 Apr 15 14:45 lost+found
[root at illustrious ~]#

...and yet the filesystems are dissimilar.  Note the stuff that is there 
on one node, but not the other, and that the date stamp for the file 
that exists on both is wrong on the second node.

Am I missing something, or am I expecting drbd to do something it's not 
capable of doing?...

Thanks,
Richard.

-- 
Alberni Valley IT Services

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