CentOS 7
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DRBD : Configure
2016/01/27
 
Configure DRBD after installing.
This example is based on the environment like follows.
+----------------------+          |          +----------------------+
| [   DRBD Server#1  ] |10.0.0.51 | 10.0.0.52| [   DRBD Server#2  ] |
|   node01.srv.world   +----------+----------+   node02.srv.world   |
|                      |                     |                      |
+----------------------+                     +----------------------+

It's necessarry the server you'd like to install DRBD has free block-device.
This example shows to configure to use a block-device "/dev/vg_r0/lv_r0".
[1] Configure DRBD on both Hosts.
[root@node01 ~]#
vi /etc/drbd.d/global_common.conf
# add follows in the disk section ( detach disk if IO errors happen )

disk {
   on-io-error detach;
[root@node01 ~]#
vi /etc/drbd.d/r0.res
# create new

resource r0 {
    # DRBD device
    device /dev/drbd0;
    # block device
    disk /dev/vg_r0/lv_r0;
    meta-disk internal;
    on node01.srv.world {
        # IP address:port
        address 10.0.0.51:7788;
    }
    on node02.srv.world {
        address 10.0.0.52:7788;
    }
} 

# load module

[root@node01 ~]#
modprobe drbd

[root@node01 ~]#
lsmod | grep drbd

drbd                  405309  0
libcrc32c              12644  2 xfs,drbd

# create DRBD resource

[root@node01 ~]#
drbdadm create-md r0
--==  Thank you for participating in the global usage survey  ==--
The server's response is:

you are the 972th user to install this version
initializing activity log
NOT initializing bitmap
Writing meta data...
New drbd meta data block successfully created.
success

[root@node01 ~]#
systemctl start drbd

 DRBD's startup script waits for the peer node(s) to appear.
 - If this node was already a degraded cluster before the
   reboot, the timeout is 0 seconds. [degr-wfc-timeout]
 - If the peer was available before the reboot, the timeout
   is 0 seconds. [wfc-timeout]
   (These values are for resource 'r0'; 0 sec -> wait forever)
...
...
To abort waiting enter 'yes' [  18]:yes
 
[root@node01 ~]#
systemctl enable drbd

[2] After configuring on both Hosts, sync data on a Host.
# current status is "Secondary/Secondary"

[root@node01 ~]#
cat /proc/drbd

version: 8.4.7-1 (api:1/proto:86-101)
GIT-hash: 3a6a769340ef93b1ba2792c6461250790795db49 build by root@node01.srv.world, 2016-01-28 14:44:07
 0: cs:Connected ro:Secondary/Secondary ds:Inconsistent/Inconsistent C r-----
    ns:0 nr:0 dw:0 dr:0 al:0 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:20938076

# get primary role and sync data

[root@node01 ~]#
drbdadm -- --overwrite-data-of-peer primary r0
# sync starts

[root@node01 ~]#
cat /proc/drbd

version: 8.4.7-1 (api:1/proto:86-101)
GIT-hash: 3a6a769340ef93b1ba2792c6461250790795db49 build by root@node01.srv.world, 2016-01-28 14:44:07
 0: cs:SyncSource ro:Primary/Secondary ds:UpToDate/Inconsistent C r-----
    ns:39144 nr:0 dw:0 dr:40056 al:0 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:20898932
        [>....................] sync'ed:  0.2% (20408/20444)M
        finish: 1:19:58 speed: 4,348 (4,348) K/sec

# after syncing, the status turns like follows

[root@node01 ~]#
cat /proc/drbd

version: 8.4.7-1 (api:1/proto:86-101)
GIT-hash: 3a6a769340ef93b1ba2792c6461250790795db49 build by root@node01.srv.world, 2016-01-28 14:44:07
 0: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r-----
    ns:20938076 nr:0 dw:0 dr:20938988 al:0 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0
[3] It's OK to configure DRBD, create file system on DRBD device and mount it to use.
[root@node01 ~]#
mkfs.xfs /dev/drbd0

[root@node01 ~]#
mkdir /drbd_disk

[root@node01 ~]#
mount /dev/drbd0 /drbd_disk

[root@node01 ~]#
df -hT

Filesystem              Type      Size  Used Avail Use% Mounted on
/dev/mapper/centos-root xfs        27G  1.7G   25G   7% /
devtmpfs                devtmpfs  2.0G     0  2.0G   0% /dev
tmpfs                   tmpfs     2.0G     0  2.0G   0% /dev/shm
tmpfs                   tmpfs     2.0G  8.3M  2.0G   1% /run
tmpfs                   tmpfs     2.0G     0  2.0G   0% /sys/fs/cgroup
/dev/vda1               xfs       497M  206M  292M  42% /boot
tmpfs                   tmpfs     396M     0  396M   0% /run/user/0
/dev/drbd0              xfs        20G   33M   20G   1% /drbd_disk

# create a test file

[root@node01 ~]#
echo 'test file' > /drbd_disk/test.txt

[root@node01 ~]#
ll /drbd_disk

total 4
-rw-r--r-- 1 root root 10 Jan 28 15:32 test.txt
[4] To mount DRBD device on the secondary Host, do it like follows.
########### on primary Host ###########

# unmount and get secondary role

[root@node01 ~]#
umount /drbd_disk

[root@node01 ~]#
drbdadm secondary r0
########### on secondary Host ###########

# get primary role and mount

[root@node02 ~]#
drbdadm primary r0

[root@node02 ~]#
mount /dev/drbd0 /drbd_disk

[root@node02 ~]#
df -hT

Filesystem              Type      Size  Used Avail Use% Mounted on
/dev/mapper/centos-root xfs        27G  1.7G   25G   7% /
devtmpfs                devtmpfs  2.0G     0  2.0G   0% /dev
tmpfs                   tmpfs     2.0G     0  2.0G   0% /dev/shm
tmpfs                   tmpfs     2.0G  8.4M  2.0G   1% /run
tmpfs                   tmpfs     2.0G     0  2.0G   0% /sys/fs/cgroup
/dev/vda1               xfs       497M  206M  292M  42% /boot
tmpfs                   tmpfs     396M     0  396M   0% /run/user/0
/dev/drbd0              xfs        20G   33M   20G   1% /drbd_disk

[root@node02 ~]#
ll /drbd_disk

total 4
-rw-r--r-- 1 root root 10 Jan 28 15:32 test.txt
 
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