7.4. Initialize DRBD

With the configuration in place, we can now get DRBD running.

These commands create the local metadata for the DRBD resource, ensure the DRBD kernel module is loaded, and bring up the DRBD resource. Run them on one node:

[root@pcmk-1 ~]# drbdadm create-md wwwdata



















  --==  Thank you for participating in the global usage survey  ==--
The server's response is:

you are the 2147th user to install this version
initializing activity log
initializing bitmap (16 KB) to all zero
Writing meta data...
New drbd meta data block successfully created.
success
[root@pcmk-1 ~]# modprobe drbd
[root@pcmk-1 ~]# drbdadm up wwwdata


















  --==  Thank you for participating in the global usage survey  ==--
The server's response is:

We can confirm DRBD’s status on this node:

[root@pcmk-1 ~]# cat /proc/drbd
version: 8.4.11-1 (api:1/proto:86-101)
GIT-hash: 66145a308421e9c124ec391a7848ac20203bb03c build by mockbuild@, 2018-04-26 12:10:42

 1: cs:WFConnection ro:Secondary/Unknown ds:Inconsistent/DUnknown C r----s
    ns:0 nr:0 dw:0 dr:0 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:524236

Because we have not yet initialized the data, this node’s data is marked as Inconsistent. Because we have not yet initialized the second node, the local state is WFConnection (waiting for connection), and the partner node’s status is marked as Unknown.

Now, repeat the above commands on the second node, starting with creating wwwdata.res. After giving it time to connect, when we check the status, it shows:

[root@pcmk-2 ~]# cat /proc/drbd
version: 8.4.11-1 (api:1/proto:86-101)
GIT-hash: 66145a308421e9c124ec391a7848ac20203bb03c build by mockbuild@, 2018-04-26 12:10:42

 1: cs:Connected ro:Secondary/Secondary ds:Inconsistent/Inconsistent C r-----
    ns:0 nr:0 dw:0 dr:0 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:524236

You can see the state has changed to Connected, meaning the two DRBD nodes are communicating properly, and both nodes are in Secondary role with Inconsistent data.

To make the data consistent, we need to tell DRBD which node should be considered to have the correct data. In this case, since we are creating a new resource, both have garbage, so we’ll just pick pcmk-1 and run this command on it:

[root@pcmk-1 ~]# drbdadm primary --force wwwdata

Note

If you are using a different version of DRBD, the required syntax may be different. See the documentation for your version for how to perform these commands.

If we check the status immediately, we’ll see something like this:

[root@pcmk-1 ~]# cat /proc/drbd
version: 8.4.11-1 (api:1/proto:86-101)
GIT-hash: 66145a308421e9c124ec391a7848ac20203bb03c build by mockbuild@, 2018-04-26 12:10:42

 1: cs:SyncSource ro:Primary/Secondary ds:UpToDate/Inconsistent C r-----
    ns:43184 nr:0 dw:0 dr:45312 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:481052
        [>...................] sync'ed:  8.6% (481052/524236)K
        finish: 0:01:51 speed: 4,316 (4,316) K/sec

We can see that this node has the Primary role, the partner node has the Secondary role, this node’s data is now considered UpToDate, the partner node’s data is still Inconsistent, and a progress bar shows how far along the partner node is in synchronizing the data.

After a while, the sync should finish, and you’ll see something like:

[root@pcmk-1 ~]# cat /proc/drbd
version: 8.4.11-1 (api:1/proto:86-101)
GIT-hash: 66145a308421e9c124ec391a7848ac20203bb03c build by mockbuild@, 2018-04-26 12:10:42

 1: cs:Connected ro:Primary/Secondary ds:UpToDate/UpToDate C r-----
    ns:524236 nr:0 dw:0 dr:526364 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0

Both sets of data are now UpToDate, and we can proceed to creating and populating a filesystem for our WebSite resource’s documents.